Microstructure Evolution and Tensile Properties of In Situ TiB2(p)/Al-Cu Composite Processed by Modified Strain-Induced Melt Activation Method with Equal Channel Angular Pressing Pre-deformation

The aim of this study is to obtain semisolid billet of the 5 wt.% TiB2(p)/Al-Cu composite with superior thixotropic behaviors using an equal channel angular pressing-strain induced melt activation (ECAP-SIMA) method. The effects of semisolid isothermal treatment (SSIT) on the microstructure evolution of the as-cast composite were investigated. The results indicate that the alpha-Al grains first partially melted followed by subsequent growth and spheroidization with increasing holding time. Ostwald ripening is the primary coarsening mechanism. However, after heating at 620-630 degrees C for 20 min, the coalescence mechanism plays a dominant role in grain growth. In addition, the TiB2 particles distributed at the grain boundaries can inhibit the coarsening of the alpha-Al grains. The optimal SSIT parameter (630 degrees C, 10 min) was chosen based on the comprehensive comparison of the microstructure under different SSIT conditions. Three different ECAP techniques were employed as the pre-deformation step for the SIMA method, resulting in the reduction of the average grain size, but increasing the average shape factor. The subsequent SSIT process can help realize the further grain refinement and slightly improve the roundness of alpha-Al grains in the ECAP-SIMA composite, thereby improving its formability. Moreover, the ECAP-SIMA composite exhibits enhanced tensile properties than those of the as-cast and SSIT composites, attributed to its refined alpha-Al grains and the uniform distribution of TiB2 particles.