Research On Aluminum Matrix Composites Reinforced With Intermetallics

In company with the extensive use of advanced technologies in automobile and motorcycle industry, engine pistons of automobile and motorcycle require higher performance of the materials in elevated temperature. Ceramics reinforced aluminum alloys have attractive properties, such as high specific strength, high modulus, high tenacity, high thermal conductivity and electric conductivity, small coefficient of expansion, good abradability, high elevated temperature strength, good surface stability, etc. However, the presence of ceramic phases also induces the problems such as processing quality of prepared material, difficulties in machine and recycling and cost control, etc. which, in turn, hindered their application. Obviously, the Al-matrix composites reinforced with intermetallic particles promise the potential of providing the properties for piston application without the difficulties encountered by the ceramic reinforced ones.Aiming at understand the morphology evolution and control of intermetallic phase, with the newly patented technique, the present work studied the morphological change of Al₃Ni phase in Al-Ni alloys through-out the atomization, powder compression and powder perform semisolid squeeze casting processes.To do so, the following research activities have been performed in present study. The effect of solidification speed on Al-Ni alloy micro-structure during gas atomization sub-rapid solidification; the effect of powder plastic deformation during pressing performing; and the influence of semi-solid squeeze casting on alloy final structure. Then, the flexural properties and hardness of the composite prepared with powder of variable diameters were examined to investigate the effect of powder's solidification speed on the flexural property and hardness of the composites. Finally, theoretical analyses and discussions were exercised to achieve better understanding of the experimental observations.Microstructure observation found that the solidification structure of Al-Ni alloy is refined and the shape of Al₃Ni phase is transformed from bulky lath-shape in conventional solidification into fine fir-tree crystal during sub-rapid solidification atomization processing; the Al₃Ni phase is then broken into small pieces during powder pressing performing process; the broken Al₃Ni phase is transformed into Al₃Ni particles with relatively uniform diameter in Al matrix during semi-solid squeeze casting.Mechanical tests show that the increase of solidification speed in terms of powder diameters raises the flexural properties and hardness of the cast composite.