Preparation, Microstructures And Mechanical Properties Of Discontinuous Non-ceramic Reinforced Aluminum Matrix Composites

Al-based composites(AMCs) reinforced with discontinous reinforcements have drawn attention in many areas, such as aerospace and automotive industry, owing to their high specific strength, high specific stiffness, high wear resistance, relatively low cost of the raw materialss and easily to be produced. Typical discontinuous reinforcement used in AMCs is ceramic, which can effectively increase the material’s strength and improve the mechanical properties. However, owing to the poor wettability between the ceramics and metal matrix, AMCs exhibit weak interface bonding which weakens the strengthening effect and decreases the plasticity. These defects give rise to the great limitation for their application. Recently, non-ceramic reinforcements, such as intermetallic compounds and metallic glasses, have been used as reinforcement in the metal matrix. These non-ceramic reinforcements have been proved to have good bonding with the metal matrix and can effectively improve the mechanical properties of the matrix. Therefore, the development of the composites reinforced with non-ceramics may provide potential solution to pave the way to dissolve the interface bonding problem and produce AMCs.In this work, pure Al was selected as the matrix for most of the AMCs, and metallic glassy particle, metallic glassy short wire, Al-based nanocrystalline particle and Ti-Al alloy particles were selected as non-ceramic reinforcements. Hot pressing, hot extrusion and Spark Plasma Sintering were chosed as producing method. The effect of the non-ceramic reinforcement on the microstructure and mechanical properties of the the composites and the strengthening mechanism and deformation mechanism were studied. The main results are as follows:(1) Al-based composites reinforced with metallic glassy particles have been synthesized by hot pressing. The composite powders were consolidated into highly dense(99%) bulk specimens by uniaxial hot pressing at temperatures within the super-cooled liquid region of the reinforcement to take advantage of the viscous flow of the glassy particles. The composites have improved yield and compressive strength compared to the unreinforced Al matrix without deteriorating the plasticity of the material. The strengthening effect obeys Iso-stress mixing model.(2) Al-based composites reinforced with samller Mg-based metallic glassy particles are synthesized by uniaxial hot pressing and their mechanical properties are analyzed. The composites have a significant strength enhancement with respect to the unreinforced ma trix. The yield stength and compressive strength increases respectively, from 63 MPa and 132 MPa for pure Al to about 203 MPa and 247 MPa for the composite with 10 vol. % reinforcement. Based on modified shear lag model incorporating the matrix strengtheni ng mechanism, beside the direct strengthening effect by the reinforcement, it reveals that the dislocation strengthening in the matrix also plays a major role for determining the mechanical properties of the composites.(3) Fe-based metallic glass short reinforced Al-based composites has been produced by hot pressing and hot extrusion. The composites have uniform distribution of the glassy particles and the good reinforcement-matrix interface. The composites have significantly imrpved strength and good plasticity. The yield stength and compressive strength increases respectively, from about 40 MPa and 132 MPa for pure Al to about 115 MPa and 245 MPa for the composite with 40 vol. % reinforcement. The strengthening effect of the fiber on the composites is strongly dependent on the fiber orientation at the shear slip plane.(4) An Al matrix composite reinforced with devitrified metallic glass particles has been prepared by hot pressing and hot extrusion. The reinforcement are distributed homogeiously in the matrix and with good interface bonding. The yield stength and compressive strength of the composite increases respectively, from about 75 MPa and 120 MPa for pure Al to about 93 MPa and 157 MPa. But the strengthening effect is obtained by sacrificing the plasticity.(5) Lightweight composites consisting of an 7075 matrix reinforced with Zr-based metallic glass fibers have been synthesized using spark plasma sintering. The results reveal that spark plasma sintering process can be used to fabricate metallic gl ass reinforced light weight composites with low porosity. The addition of metallic glass fibers and particulate reinforcement in the Al based matrix significantly improves the strength, the yield strength increases from ~167 for pure Al to ~362 MPa for the composite which also keeps good plasicity.(6) Lightweight composites consisting of an Al-12 Si matrix reinforced with Ti-Al-NbMo-B(TNM) crystalline particles have been fabricated by powder metallurgy through hot pressing and hot extrusion. The results reveal that the tensile properties of the composites are effectively improved by the addition of the reinforcing TNM particles. The yield strength increases from about 104 MPa for Al-12 Si to about 125 MPa and 150 MPa for the composites reinforced with 20 vol. % and 40 vol. % TNM respectively.(7) Among the different reinforcement reinforced Al-based composites, Mg58Cu28.5Gd11Ag2.5 metallic glassy particle reinforced Al-based composite exhibits both high strength and good plasticity.