Aluminium and Magnesium Based Metal Matrix Composites Kompoziti na osnovi Al in Mg K. U. Kainer1, Technische Universitat Clausthal-Zellerfeld, Germany Prejem rokopisa - received: 1996-10-01; sprejem za objavo - accepted for publication: 1996-11-04 In motor-cars metal matrix composites (MMCs) are employed in braking systems and engine components. Other applications for these materials have been developed in energy and in information applications. The potentional of composite materials is very great because the properties can be tailored according to the application. There are many possible material combinations and processing techniques which can be employed. For structural applications standard iight metal are often strengthened by ceramic fibres or particles. The performance and potential of composites will be discussed using examples of reinforced aluminium and magnesium alloys. Key words: Al and Mg based MMCs, Al and Mg alloys, SiC and Alz03 as reinforcement, properties, applications, processing techniques Kompoziti s kovinsko osnovo, ojačani s keramičnimi delci ali vlakni se danes že uporabljajo kot deli zavornega sistema in motorjev z notranjim izgorevanjem. Razvite so tudi posebne vrste teh materialov, ki so uporabni na področju energetike in informatike. Uporabnost kompozitnih materialov je vsestranska, ker lahko njihove lastnosti prilagajamo potrebam uporabe. Možne so številne kombinacije materialov (kovinska osnova / keramična ojačitev) in postopkov njihove izdelave. Kompoziti, ki se uporabljajo kot konstrukcijski materiali so najpogosteje sestavljeni iz lahke kovinske osnove in keramičnih delcev ali vlaken. Prispevek obravnava predvsem dosežene lastnosti in možnosti uporabe kompozitov z osnovo iz Al ali Mg zlitin, ki so diskontinuirno ojačane z SiC ali AI2O3 delci oziroma kratkimi vlakni. Ključne besede: kompoziti s kovinsko osnovo, Al in Mg zlitine, SiC in AI2O3 kot ojačitvena faza, lastnosti, uporaba, postopki izdelave 1 Introduction The strenuous efforts to develop metal matrix composites vvith light metal matrices in the eighties have paid off vvith successful applications in automobile and transport systems. Worthy of mention are partially reinforced pistons, hybrid reinforced engine blocks for cars or trucks as vvell as particle reinforced brake discs for light lorries, motocycles, cars or rail vehicles. Further fields of applications are military aircraft and space craft. The in-novative materials are interesting possibilities in the development of modern materials because the properties of MMCs can be tailored for a particular application and hence MMCs can fulfill ali requirements of the designer. Such materials become important vvhen the property profile cannot be achieved by the conventional light metal alloys. The specific strength as outstanding advantage of light metal MMCs is hovvever under pressure from com-peting technologies such as povvder meta!lurgy of polmer technology. The advantages of composites are only realised if a resonable cost performance ratio is achiev-able on production of the component. In this respect it is important for economic and ecological reasons to recycle scrap components, production vvaste, etc. The aims in the reinforcement of metal matrix func-tional or structural materials are on the one hand the op-timisation of some critical properties at the same time as maintaining other properties and on the other hand a 1 Dr.-Ing. habil. K. U. KAINER Tcchniscbe Universitat Clauslhal ■Institut lur VVerkštofflcunde und VVerkstofftechnik. Clausthal-Zellerfeld. Germany complete change in the property profile of a class of materials. The reinforcement of light metals opens, for ex-ample, an extension of the application potential vvhere vveight reduetion of components is very desirable at the same time as optimisation of component properties. The development aims of light metal matrix composites thus can be sumarised as follovvs: - inerease in yield strength, ultimate tensile strength and fatigue strength at room temperature vvhilst maintaining minimum values of ductility or toughness, - inerease in hot strength, fatigue strength and creep resistance at elevated temperatures compared to conventional materials, - reduetion in the coefficient of thermal expansion of light metal alloys to values comparable vvith steels, - improvement in the stability of light metals to temperature changes, - improvement in damping behaviour, - improvement in the vvear resistance through addition of hard materials, - improvement in vveight specific properties (strength and E-modulus). Discontinuous particle, fibre or vvhisker reinforced light alloys are most likely to fulfill design eriteria because the components are relatively cheap and production of components in large numbers is possible. Further advantages are the relatively high isotropy of properties compared to the long continuous fibre reinforced light metals and the possibility of further forming by forging and machining. 2 Combination of materials for light alloy compos-ites The obvious candidates for light metal matrices for composite materials are the easily workable, conven-tional a!loys. Particulary when powder metallurgical (P/M) production techniques are employed it is possible to consider special alloys with specific compositions. P/M technology allows the use of alloys with super sa-torated or metastable phases. The alloys are free from segregation problems as often observed after conven-tional solidification. Examples of extensively investigated matrix alloys are1"8: Conventional Casting Allovs: Al allovs: AlSil2CuMgNi AlSi9Mg AlSi7 (A 356) Mg allovs: MgA19Znl (AZ91) MgA12RE2Zrl (MSR, QE 22) Conventional wrought allovs: Al allovs: AlMgSiCu (6061) AlCuSiMn (2014) AlZnMgCul 5 (7075) Mg allovs: MgA13Zn (AZ 31) MgZn6Zr (ZK 60) MgZn6Cu3 (ZC 63) Special allovs: Al allovs: Al-Cu-Mg-Li (8090) Mg allovs: Mg99,5 + RE, Ca, Zr, Ba. Br, Sb or Sn (1-2.4%) A wide variety of reinforcement materials are avail-able vvith a vvider range of properties. The choice depends on the method chosen for production and on the matrtx alloy system. In general the requirements are: - lovv density, - mechanical compatability (a thermal coefficient of expansion vvhich matches the matrix), - chemical compatability, - thermal štabi lity, - high elastic modulus, high compressive and tensile strength, - good workability, - economicy. These demands can be fulfilled virtually only by in-organic reinforcing materials. Often only ceramic particles or fibres or carbon fibres are used to reinforce met-als. The use of metallic fibres results in prohibitive increases in density. Which component is chosen depends on the matrix material and the property profile of the particular application. Information of available particles, short fibres, vvhiskers and continuous fibres for reinforcement of metals is collected in Table 1 and in references910. The preparation, vvorking and means of applications of the various reinforcements depends on the method chosen to produce the composite (see1). A combinated application of tvvo and more reinforcement material is possible (hybrid technique)1-9. 3 Production of light metal composites There are several possible methods of producing semi finished material and components in light metal composites, vvhich depend primarly on the component geometry and the material systems (matrix / reinforcement). The process must be divided into preparation of suitable starting material, production of the semi finished material or component and finishing operations. For eco-nomic reasons near net shape production should be at-tempted to minimise mechanical finishing operations. In general the follovving production techniques are available: • Casting techniques - infiltration of short fibres, particle or hybrid pre-forms by squeeze casting, vacuum infiltration or pressure infiltration1'4'7'8, Table 1: Examples of particles, whisker, continuous and discontinuous fibres used a reinforcements in metal alloys (*CTE = coefficient of thermal expansion, nPAN based fibres, 2lpitch based fibres) reinforcement producer diameter densitv E-modulus tensile strength CTE* (10"6K"') (pm) (gcm5) (GPa) (MPa) axial FP OC-AI2O3 Du Pont 20 3.9 380 > 1400 7.6 Altex alumina fibre Sumitomo 17 3.2 300 2000 8.8 Nicalon SiC-fibre Nippon Carbon 15 2.6 185 2700 3.5 Torayca T-300" Toray 7 1.8 230 3530 -0.26 Torayca M-4011 Toray 5.5 1.8 392 2650 -1.3 Thornel P 752) Amoco 10 2.0 520 2370 -1.4 Saffil RF disk a-Al203 ICI plc. 1-5 3.3 300 2000 4.7 SiC-whiskers Silar DWA Composites Specialities 0.6 3.2 690 6900 4.1 SiC-particles Norton AS, ESK. Kempten various 3.2 ca.400 - 4.7 alumina platelets Elf, ESK, Kempten various 3.9 ca.380 - 3.6 alumina particles H.C. Starck, ESK. Kempten various 4.0 ca.380 - 9.5 'P' 4 9 * Figure 1: Collection of typical microstructures of various light metal composites as a function of reinforcement and production process. a) AI2O3 short fibre reinforced magnesium. b) AbO.i-SiC hybrid reinforced magnesium, c) SiC particle reinforced aluminium (chill čast), d) SiC particle reinforced aluminium (pressure die čast), e) SiC particle reinforced aluminium (čast and e.\truded), f) SiC particle reinforced aluminium (extruded povvder blend). g) SiC particle reinforced magnesium (spray formed), h) SiC particle reinforced magnesium (spray formed and extruded) 11 12 - reaction infiltration of fibre or particle preforms ' , - production of prematerial by stirring particles into metallic melts vvith subsequent sand casting, chill casting or pressure casting2,3. • Powder metallurgy techniques - extrusion or forging of metal povvder - particle mix-tures5'6, - extrusion or forging of spray formed semi finished material1'13'14. • Further processing of semi finished čast material by thixocasting or forming, extrusion15, forging, cold forming or superplastic forming, • Joining or vvelding of semi finished products, • Finishing by machining. 4 Structure and properties of light metal composites The structure of composites is determined by the na-ture and shape of the reinforcing components, their distribution and orientation by the production process. Typi-cal microstructures of various short fibre and particle reinforced light metals are shown in Figure 1. In the čase of short fibre reinforced composites a planar iso-tropic distribution of the short fibres is formed as a result of the production of the fibre preform. The pressure sup-ported sedimentation technque leads to a layer like structure (Figures la & b)10. The direction of infiltration is generally normal to these planeš. The čast particle reinforced light metals show, depending on the vvorking processing, typical particle distributions. Gravity čast material exhibit as a result of the casting conditions particle free regions (Figure lc), vvhereas pressure die čast A 500 i 400 E E Z 300 si CD S 200 -4—» (/) U 100 0 0 0 100 200 300 400 °c temperature -► Figure 2: Comparison of the temperature dependence of the tensile strength of the unreinforced and reinforced piston alloy AlSil2CuMgNi (KS 1275)7 a) KS 1275 vvith 20 vol.% SiC vvhiskers, b) KS 1275 vvith 20 vol.% AI2O3 short fibres, c) KS 1275 unreinforced materials shovv a much better particle distribution (Figure ld). An even distribution is achieved by extrusion of semi finished material (Figure le). An extremely homo-geneous particle distribution is obtained by extrusion of mixed povvders or spray formed materials (Figures 1 f-g)- Properties of short fibre reinforced aluminium An increase in strength with increasing fibre content in short fibre reinforced aluminium is actually observed as the example AlSil2CuMgNi vvith 20 vol.% AI2O3 shovvs in Figure 2. Composites of light metal casting al-loys is not made just to increase only the strength. The effect alone vvould not be justifiable economically. The improvement of the properties at high temperature vvith a doubling of the strength (Figure 2) and the rotating bending fatigue strength at 300°C (Figure 3), opens up possibilities for use as piston material or cylinder liners. A dramatic increase of the thermal shock resistance can be achieved at temperature of 350°C as is shovvn in Figure 4. Properties of particle reinforced aluminium In general addition of particles to light metals, such as magnesium and aluminium increases the elastic modulus, yield strength, ultimate tensile strength, the hardness and the vvear resistance and also decreases the coefficient of the thermal expansion. The degree of improvement of these properties depends on the volume fration of the particles and the chosen means of production. Tables 2 and 3 shovv a collection of properties of various particle reinforced aluminium alloys. The particle volume fraction in stirred in particle reinforced Al al-loys is limited to about 20 vol.%. This limit is imposed by the process. A maximum tensile strength of over 500 MPa and E-moduli of 100 GPa are possible for this particle content. Higher particle contents can be achieved by £ 150 a C S! «1 ra o o. 3 S s —100 ™ 5 - n | b S 50 O) C n o i. 0 0 100 200 300 °C 400 temperature Figure 3: Change in the rotating bending fatigue strength of the unreinforced and reinforced (20 vol.% AI2O3) piston alloy AlSil2CuMgNi (KS 1275) vvith increasing temperature® (GK = chill čast GP = squeeze čast) - 1- 1 1 l Ng=2.5* 10' P„=50% N . N ' N ' . ............ "............GP - KS1275/20%AI20^ GP -KS1275 ---GK -KS1275 "*-• 1 i i i O 2000 4000 6000 1000 3000 5000 temperature cycls-► Figure 4: Temperature shock resistance of the fibre reinforced piston alloy AlSil2CuMgNi as a function of the fibre content for a temperature of 350°C7: a) unreinforced. b) 12 vol.% AI2O3 short fibres, c) 17.5 vol.% AJ2O3 short fibres, d) 20 vol.% AI2O3 short fibres infiltration of particle preforms with higher particle volume fraction. The materials then assume increasingly the characteristics of ceramics. On tensile loading premature failure occurs. The small thermal expansion is an excel-lant characteristic despite the metallic features. There is a limit to the particle content of about 13-15 vol.% also for spray formed materials. The use of special alloys e.g. with lithium additions can nevertheless lead to high specific properties. If povvder metallurgical tech-nique involving extrusion and forging are applied then the particle content can be increased to more than 40 vol.%. As the result of high particle content and the re-sultant fine grain of the matrix very high strength of up to 760 MPa, very high E-Moduli of 125 GPa and lovv coefficients of expansion of 17 x 106K"' can be achieved. Unfortunately the elongation to fracture and the fracture toughness deteriorate. The values lie, hovv-ever, in part above those for casting alloys. Properties of discontinuously reinforced magnesium al- loys In general the strengthening effects in discontiuous reinforced composites is smaller than in continuous fibre reinforced materials but the properties are more iso-tropic. In the follovving the properties of short fibre or particle reinforced magnesium composites are listed. Table 4 shows the 0.2 yield strength, the temperature de-pendence of the ultimate tensile strength and the ductil-ity of different magnesium alloys reinforced vvith 20 vol.% Saffil short fibre. The properties are compared vvith of these of unreinforced alloys. Information about hardness, Young's modulus and coefficient of thermal ex-pansion (CTE) are included. The results shovv that the main advantages of this type of composite material are the high specific strength at elevated temperatures, the increase of Young's modulus and the reduction of the CTE. The improvement of the properties depends on the volume content of the short fibres. In the range of 15 -22 vol.% short fibres the most promising properties vvere measured416. With a higher fibre content problems in the infiltration arises vvhich reduces the strength and ductil-ity of the composites. Table 2: Selected properties of typical čast aluminium composites, prepared b^chill, pressure die casting or reaction infiltration2,3,11. (T6 = solution annealed and aged, T5 = aged; 'after ASTM G-77: čast iron 0.66 mm3; *CTE = coefficient of thermal expansion, a) after ASTM E-399 and B-645; b) after ASTM E-23), n.i. = no information Material Identification Composition Yield stress (MPa) Tensile strength (MPa) Elongation to fracture (%) Young's modulus (GPa) a) Fracture toughness. b) impact strength VVear' volume decrease (mm3) Thermal conductivity 22°C (cal/cm s K) CTE" 50- 100°C (KTK'1) Gravity casting (chill casting) a) (MPa m1'2) A356-T6 AlSi7Mg 200 276 6.0 75.2 17.4 0.18 0.360 21.4 F3S.10S-T6 AlSi9MglOSiC 303 338 1.2 86.9 17.4 n.i. n.i. 20.7 F3S.10S-T6 AlSi9Mg20SiC 338 359 0.4 98.6 15.9 0.02 0.442 17.5 F3K.10S-T6 AlSilOCuMgNilOSiC 359 372 0.3 87.6 n.i. n.i. n.i. 20.2 F3K.20S-T6 AISi 10CuMgNi20SiC 372 372 0.0 101 n.i. n.i. 0.346 17.8 Die casting b) (J) A390 AlSil7Cu5Mg 241 283 3.5 71.0 1.4 0.18 0.360 21.4 F3D.10S-T5 AISi 1 OCuMnNi 1 OSiC 331 372 1.2 93.8 1.4 n.i. 0.296 19.3 F3D.20S-T5 AlSil0CuMnNi20SiC 400 400 0.0 113.8 0.7 0.018 0.344 16.9 F3N.10S-T5 AlSilOCuMnMglOSiC 317 352 0.5 91.0 1.4 n.i. 0.384 21.4 F3N.20S-T5 AISi 10CuMnMg20SiC 338 365 0.3 108.2 0.7 0.018 0.401 16.6 Reaction infiltration Bending strength (MPa) Density (g/cm3) a) (MPa m"2 ) MCX-693™ Al+55-70 % SiC 300 2.98 255 9.0 n.i. 0.430 6.4 M.CX-724™ Al+55-70 % SiC 350 2.94 226 9.4 n.i. 0.394 7.2 MCX-736™ Al+55-70 % SiC 330 2.96 225 9.5 n.i. 0.382 7.3 Table 3: Properties of aluminium wrought alloy composites, manufactures information after5-613-15. (T6 = solution annealed and aged), "after ASTM G-77: čast iron 0,66 mm3; **CTE = coefficient of thermal expansion, n.i. = no information. Material Identification Yield stress (MPa) Composition Tensile strength (MPa) Elongation lo fracture (%) Young's modulus (GPa) a) Fracture toughness. b) impact strength Wear volume decrease (mm3) Thermal conductivity 22°C (cal/cm s K) CTE" 50-100°C (10"6K"') Čast starting material (extruded or forged) 6061-T6 AlMglSiCu 355 375 13 75 30 10 0.408 23.4 6061-T6 + 10% AI2O3 335 385 7 83 24 0.04 0.384 20.9 6061-T6 + 15% AI2O3 340 385 5 88 22 0.02 0.336 19.8 6061-T6 + 20% AI2O3 365 405 3 95 21 0.015 n.i. n.i. Powder metallursicallv prepared starting material (extruded) 6061-T6 AlMglSiCu 276 310 15 69.0 n.i. n.i. n.i. 23.0 6061-T6 + 20% SiC 397 448 4.1 103.4 n.i. n.i. n.i. 15.3 6061-T6 + 30% SiC 407 496 3.0 120.7 n.i. n.i. n.i. 13.8 7090-T6 AlZn8Mg2Col.5Cul 586 627 10.0 73.8 n.i. n.i. n.i. n.i. 7090-T6 + 30% SiC 676 759 1.2 124.1 n.i. n.i. n.i. n.i. 6092-T6 AlMglCulSil7.5SiC 448 510 8.0 103.0 n.i. n.i. n.i. n.i. 6092-T6 AlMglCulSi25SiC 530 565 4.0 117.0 20.3 n.i. n.i. n.i. Spray formed starting material (extruded) 6061-T6 + 15% AI2O3 317 359 5 87.6 n.i. n.i. n.i. n.i. 2618-T6 + 13% SiC 333 450 n.i. 89.0 n.i. n.i. n.i. 19.0 8090-T6 AlLi2.5CuMg 480 550 n.i. 79.5 n.i. n.i. n.i. 22.9 8090-T6 + 12% SiC 486 529 n.i. 100,1 n.i. n.i. n.i. 19.3 Table 4: Properties of short as čast fibre reinforced magnesium composites (CTE = coefficient of thermal expansion, n.d. = not determined, rt = room temperature, 0.2 YS = 0.2 yield strength. UTS = ultimate tensile strength)4 Cp-Mg AS 41 AZ 91 QE 22 matrix comp. matrix comp. matrix comp. matrix comp. 0.2 YS (MPa) (rt) 70 220 125 240 160 230 180 250 UTS (MPa) (rt) 80 240 193 270 220 280 250 300 Elongation (%) (rt) 5.0 2.2 9.0 1.0 4.8 1.8 4.5 1.6 Young's modulus 46 56 49.8 77.7 46 64 46 74 (GPa) UTS (100°C) (MPa) 65 240 175 250 200 270 240 285 UTS (200°C) (MPa) 45 180 150 240 120 220 200 245 UTS (300°C) (MPa) 30 120 n.d. n.d. 60 130 125 180 Vickers hardness 40 75 n.d. n.d. 65 140 75 125 HV10 (kp/mm2) CTE (10"6K"')* 26.5 21.5 24.0 18.0 27.0 20.5 26.0 20.0 The second group of discontinuous reinforced composites are particle reinforced magnesium alloys. The high range of properties is achieved by the limitless vari-ation possibilities of alloys, type of particle and produc-tion techniques. In general only a modest improvement in the strength by addition of particles is observed. But with the increase in hardness, wear resistance and Young's modulus together with the reduction of the CTE the material becomes interesting for commercial applica-tion17. The Tables 5 and 6 show the propety profiles of different produced particle reinforced magnesium composites. The SiC particles used for composite materials in Table 5 have irregular blocky shape. These particles were treated to achieve a smooth surface without sharp tips. The result are composites with high strength and very good ductility combinated with high hardness, Young's modulus and low CTE values. The P/M produc-tion technique unfluences the properties of the particle reinforced composites, as shown in Table 6. The highest strength but with low ductility is measured for spray formed and extruded composites. The best properties were achieved for direct powder forged composites, a near net shape production technique. With a special pre-form technique it is possible to produce particle or hy-brid reinforced composites by squeeze casting. The properties of material system investigated are listed in Table 5. As reinforcement a SiC-particles-fibre hybrid preform and aluminia platelets were used. The material shows lower strength and ductility due to the solidification mi- Table 5: Properties profile of P/M produced or squeeze čast QE 22 composites with different additions of reinforcement (SiC-particles, hybrid SiC-AbCb-preforms, Al203-platelets in vol.%)17 0.2 UTS Elonga- Young's Brinell CTE rt-yield (MPa) tion to modulus hardness 30Q°C strength fracture (GPa) HB31,25/(10"6K"') _(MPa)_(%}_2J_ Powder metallurgy produced composites (T6) condition_ P/M QE 22 - T6 175 260 18 43 70 27.1 QE 22 + 10% SiC 200 265 10 48 87 21.4 QE 22 + 15% SiC 210 290 10 58 95 20.0 QE 22 + 20% SiC 225 315 6.5 66 120 18.2 QE 22 + 25% SiC 245 325 4.0 73 108 16.6 Sgueeze čast composites Sq/C QE 22 - T6 185 262 5.2 69 48 27.0 QE 22+20%SiC 265 285 2.4 74 120 18.9 hybrid QE 22+25%SiC 270 282 1.0 80 125 17.5 hybrid QE 22 + 20% 177 250 1.0 85 110 19.8 AhO? platelets crostructure which is different to the rapid solidified structure by use of P/M technologies. Table 6: Influence of the production technique on the properties of P/M QE 22+15 vol% SiC-particles-composites Unrein-forced QE22 Spray formed and extruded Extruded powder blends Forged powder blends 0.2 yield strength (MPa) 180 300 250 220 UTS (MPa) 252 320 300 300 Elongation to fracture (%) 16.0 1.0 4.0 4.5 Vickers hardness (HV10 82 92 88 94 kp/mm2) Young's modulus (GPa) 46 69 70 79 CTE (10"6K"') 27.1 20.5 21.1 20.8 5 Possible uses and applications for metallic matrix composites Light metal composites are interesting materials for automobile components in the engine (oscillating parts: valve system, connecting rod, pistons and piston pin; covers: cylinder head, crankshaft main bearing; motor block: partially reinforced cylinder liner). An example for a successful application involving aluminium composites is the partially reinforced short ftbre aluminium pistons in which the combustion chamber is reinforced with AI2O3 short fibres. Comparable component properties are only possible in powder metallurgical produced aluminium alloys or in iron pistons. The reason for the use of composites are, as explained above, improved high temperature properties. Similar considerations ap-ply to partially reinforced cylinder blocks. In this čase the critical areas, the bridges and cylinder surfaces are reinforced. The same applies to the reinforcement of aluminium cylinder heads where cracking in the combustion chamber is the Iife limiting factor. Figure 5 shows the development goal on increasing the component temperature for reinforced aluminium cylinder heads. % 100 80 60 a) I 40 CD ~ 20 I N. \ \ \ a S \ b 220 240 260 280 300 part temperature 340 Figure 5: Component Iife for aluminium cylinder heads for car diesel engines (The Iife fimiting factor is cracking in the combustion chamber area)7 Potential applications can be found also in the pro-pulsive components e.g. transverse link and particle reinforced brake discs. The latter are also employed in rail transport (tube trains, railway trains). In air and space applications, the high strength, the high E-modulus, the low thermal coefficient of expansion, the temperature stabillity and the high conductivity of reinforced light metals compared to polymer materials make composites interesting for stiffening parts, load bearing tubes, rotors, covers, and containers and supports for electronic de-vices. A collection of potential actual applications of the various metal matrix components (MMCs) is given in Table 7. In history, the first technical applications of MMCs were in the fields of energy and information engineering, e.g. carbon brushes (Cu-graphite) or contact materials. There is stili scope for further development in conductor materials, support materials for printed circuits or structures for electronic components. Further economically interesting applications are to be found in leisure applications e.g. extruded and welded particle reinforced alu- Table 7.1: Potential and actual technological applications of metal matrix composites (part 1) Application Reguired propertv Material system Production method automobile and commercial vehicles stiffeners, connecting rod, frames, piston, piston pins, valve spring retainer, brake disks, brake, brake linings, drive shaft. accumulator plate_ high specific strength and stiffness, temperature stability, low coefficient of thermal expansion, wear resistance, thermal conductivity. high stiffness, creep resistance Al-SiC, AI-AI2O3, Mg-SiC, Mg-Al203, discontinuous reinforcements. Pb-C, Pb-A12Q3 melt infiltration, extrusion, forging, gravity casting, pressure die casting, squeeze-casting. melt infiltration militarv and civil aircraft supporting tubes, stiffeners, high specific strength and wings- and gear boxes, ventila- stiffness, temperature stability, tion and compressor blades. fracture toughness, fatigue resistance turbine blade high specific strength and stiffness, temperature stability, fracture toughness, fatigue ____resistant. Al-B, Al-SiC, Al-C, Ti-SiC, AI-AI2O3, Mg-Al203, Mg-C continuous and discontinuous reinforcements. W, superalloys, intermetallics e.g. NijAl, Ni-Ni3Nb melt infiltration, hot pressing, diffusion welding and soldering, extrusion, squeeze-casting. melt infiltration, directional solidification of near net shape components Table 7.2: Potential and actual teehnological applications of metal matrix composites (Part 2) Application Required property Material system Production method space frames, stiffeners, antennas, high specific strength and joints, bolds. stiffness, temperature stability, lovv coefficient of thermal expansion, thermal conductivity Al-SiC, Al-B, Mg-C, Al-C, Al-A];C>3, continuous and discontinuous reinforcements. melt infiltration, extrusion, diffusion bonding and joining (spatial structures) energy eneineering (electrical contacts and conductive material) carbon brushes electrical contacts superconductor high electrical and thermal conductivity wear resistance high electrical conductivity, temperature and corrosion resistance, switch capacity, resistance to burn. superconductivity, mechanical strength, ductility._ Cu-C Cu-C, Ag-Al203, Ag-C, Ag-Sn02, Ag-Ni Cu-Nb, Cu-NbjSn. Cu-YBaCO melt infiltration, powder metallurgy. melt infiltration, powder metallurgy, extrusion, hot pressing extrusion, powder metallurgy, coating technigues._ other applications spot welding electrodes bearings resistance to burn. load bearing capacity, wear resistance. Cu-W Pb-C, bronze-Teflon powder metallurgy, infiltration. powder metallurgy, infiltration minium-mountain bike frames and golf clubs with particle reinforced inserts. Baseball bats are another possible application because the higher damping would result in a completely different striking behaviour. 6 Recycling The necessity of integrating production waste and scrap of newly developed materials is of particular im-portance. Since ceramic materials are used in the form of particles, short fibres or continuous fibres as reinforcement it is not possible to separate the components vvith aim of reutilising of matrix and the reinforcement. But conventional melting techniques can be employed to re-cover the matrix alloy. In the čase of čast or povvder metallurgical^ produced discontinuously reinforced light metals (short fibre or particle) it is possible under certain conditions to reuse the svvarf. This is particular so for particle reinforced aluminium casting alloys where no problems arise by remelting the svvarf and directly use of the čast ingots vvithout modification. The paper18 pro-vides an overvievv of the various recycling concepts for light alloy matrix composites taking into account alloy composition, reinforcement type and the production and vvorking history. 7 Conclusion The development of metal matrix composites can be used to improve critical properties of metal alloys e.g. high temperature strength, stiffness, vvear resistance and thermal expansion. With high variability of materials combination and manufacturing techniques it is possible to produce tailor-made materials. Which combination and production techniques are choosen depends on the requirement of the possible application. The production processes allovv the manufacture of semi-finished prod-ucts or near net shape parts. 8 Literature 'K. U. Kainer (ed.): Metallische Verbundwerksoffe, DGM Informa-tionsgesellschaft. Oberursel, 1994 2 DURALCAN Composites for Gravity Castings, Duralcan USA, San Diego, 1992 3 DURALCAN Composites for High-Pressure Die Castings, Duralcan USA, San Diego, 1992 ""K. U. Kainer: Guss Produkte 91, Verlag Hoppenstedt, Darmstadt, 1991,261-262 5 C. W. Brovvn, W. Harrigan, J. F. Dolowy, Proc. Verbundvverk 90, De-mat, Frankfurt, 1990, 20.1. - 20-15 6Manufactures of Discontinuously Reinforced Aluminium (DRA), DWA Composite Specialities, Inc., Chatsvvorth USA, 1995 7W. Henning, E. Kohler, Maschinenmarkt, 101, 1995, 50-55 8 S. Mielke, N. Seitz, Grosche, Int. Conf.on Metal Matrix Composites, The Institute of Metals, London, 1987, 4/1-4/3 '' K. U. Kainer, Keramische Partikel, Fasern und Kurzfasern fiir eine Verstarkung von metallischen Werkstoffen in Metallische Ver-bundwerkstoffe, K. U. Kainer (ed.), DGM Informationsgesellschaft, Oberursel, 1994, 43-64 10 H. Hegeler, R. Buschmann, I. Elstner: Herstellung, Eigenschaften und Anvvendungen von Kurz- und Langfaserpreforms in Metallische Ver-bundwerkstoffe, K. U. Kainer (ed.), DGM Informationsgesellschaft, Oberursel, 1994, 101-116 1' Lanxide Electronic Components, Lanxide Electronic Components, Inc., Nevvark USA, 1995 12 C. Fritze, K. U. Kainer: Proc. Conf. Verbundwerkstoffe und Werkstoff-verbunde, G. Ziegler (ed.) DGM Informationsgesellschaft, Oberursel, 1996, 483-486 13 A. G. Leatham, A. Ogilvy, L. Elias, Proc. Int. Conf. P/M in Aero-space, Defence and Demanding Applications, MPIF, Princeton, USA, 1993, 165-175 14 Cospray Ltd. Banbury, U.K., 1992 ,5Keramal Aluminium-Verbundvverkstoffe, Aluminium Ranshofen GmbH, Ranshofen, Austria, 1992 16 K. U. Kainer, B. L. Mordike, Metali, 44, 1992, 436-439 17 K. U. Kainer, Proc. Int. Conf. New and Alternative Materials for the Transportation Industries, I SATA, Croydon, 1994, 463-470 18 K. U. Kainer: Konzepte zum Recycling von Metallmatrix- Ver-bundvverkstoffen, in press Proc. Recycling von Verbundvverkstoffen und Werkstoffverbunden, DGM Informationsgesellschaft, Frankfurt