Microstructural Evolution During Reheating Of In-situ Reaction Cast TiC_p /7075Al Semi-Solid Ingots

Metal semi-solid forming technology combining liquid and solid metal forming of favorable conditions, with many excellent features, is considered as is one of the 21st century metal manufacture emerging technologies, and given priority to development in our country high-tech industry recently. The most widely applied semi-solid processing technique is often called thixoforming, which includes three major steps, i.e. preparing of blank perform, reheating and semi-solid forming. Currently, in order to obtain a reasonable solid-liquid ratio under reheating conditions, the grains over-grown and coarsening phenomenon are universal, This will produce harmful effects to forming document function , hasn′t found the effective solution yet. Therefore, how to keep the equiaxed grain features with an average grain size is the key to semi-solid forming technology.The TiC_p/7075Al semi-solid ingots have been fabricated by in-situ reactive near-liquidus casting in this work. The effect of X%TiC_p/7075Al semi-solid ingots (X=1.5%,3.4%,4.4%) on the reheating structure was analyzed and compared with 7075 alloy which was prepared by near-liquidus casting. The microstructure of reheated and as-cast specimens was characterized using OP, SEM and TEM. The grain size was measured using Image Tool and a mean linear intercept method. By way of measuring the relation between average equal-area-circle diameter and different reheating temperatures and different holding time were measured actually, the grain of TiC_p/7075Al semi-solid ingots growth kinetics model was establish. The actual measuring values and theoretical values were compared.The result shows that the in-situ TiC particles can not only keep near-liquidus cast 7075 Al alloy with fine and globular microstructure, but also control evidently grains growth by pinning effect during reheating and improvement the round degree and homogenization of grains. The weight fraction of in-situ TiC particles up to 4.4 %, the grain growth exponent (n) for Arrhenius equation was increased from 2 to 3, which indicates that the in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solid state. This time, the error value does not exceed 10%, the model can better reveal the law of grain growth during reheating. It indicates that the TiC_p/7075Al semi-solid ingots were very suitable for thixoforming.