IN-SITU PROCESSING AND PROPERTIES OF TiB₂/ZA27 COMPOSITES

In-situ TiB₂ particles reinforced ZA27 composites were produced by two steps. As beginning, the reaction of creating TiB₂ was processed in melting Al. After that, the second step, as a master alloy, TiB₂/Al material was used to fabricate TiB₂/ZA27 composites. It is found that the TiB₂ particles whose size is less than 3 μm distribute in ZA27 matrix uniformly and the shape of them is equiaxed. The test results show that the tensile strength and hardness of the composites are enhanced observably following the refinement of matrix grain with the increase of TiB₂ particles. For example, the tensile strength of the 2.1%TiB₂/ZA27 composite is as high as 472 MPa when the hardness is 126 HB. The thermal expansion coefficient of 2.1%TiB₂/ZA27 decreases compared with that of ZA27 alloy while the elastic modulus increases. At the same time, the ductility of the composites has not deteriorated and the elongation is also raised slightly.