Effect of strain-induced melt activation process and thixoforming on microstructure and mechanical properties of 319 aluminum alloy

Abstract

The effect of the thixoforming process on the microstructure and mechanical properties of modified and grain refined 319 aluminum alloy has been investigated. The strain-induced melt activated (SIMA) process has been applied to achieve proper microstructure for semi-solid processing. As-cast 319 aluminum parts have a dendritic microstructure and mostly contain defects such as porosity and shrinkage. The semi-solid treatment process eliminates these defects and is used to obtain a spherical structure with enhanced mechanical properties. Image analysis of the semi-solid treated specimens showed that the best sample had the highest amount of α-Al particle sphericity (0.88) and the lowest average equivalent diameter of α-Al phases (56 µm) under the conditions of 30% of the hot pre-deformation at 560 °C and isothermal holding time of 30 min. The specimens were thixoformed after the SIMA process to generate near-net-shape pieces. The thixoforming process enhanced the hardness of 319 aluminum alloy from 78.1 ± 1.91 HB to 115.6 ± 1.73 HB. Based on the tensile test results, the thixoforming process raised the ultimate tensile strength, yield strength, elongation, and toughness by 30%, 69%, 180.5%, and 189%, respectively, compared to the as-cast state.