MACHINABILITY OF ALUMINUM-ALLOYS REINFORCED WITH SILICON-CARBIDE PARTICULATES

Cold isostatic pressed then hot extruded Al-Li alloys reinforced with 10-20 wt% SiC particulates have been produced successfully. Such compo sites are well-known for their high specific strength, high wear resis tance, but poor machinability. Analytical based published papers on th e machinability of metal. matrix composites ate very limited. This stu dy utilizes Taylor's tool life equation to model a facing process such that the performance of a single-point cutting tool can be predicted and optimized for different cutting conditions. Different approaches b ased on linear accumulative damage results in two different models. Th e models were first verified with data from the turning and facing of steel, then applied to study the machinability of AI-Li SiCP composite s. Performances of tested tool materials (i.e. high speed steel, titan ium nitride coated high speed steel, tungsten carbide, cubic boron nit ride (CBN), and polycrystalline diamond) used in machining these compo sites were ranked. Sub-surface damage of faced samples was assessed by measuring the micro-hardness of the plastically deformed matrix, and microscopically examining cross sections of chemically etched samples. CBN and diamond tools fracture the SiC particulates along their cryst allographic planes and induce little damage in the matrix, while other tools not only delaminate the particulates from the matrix, but also roughen the particulates, and significantly deform the matrix.