Microstructure and Induced Defects of 6061 Al Alloy after Short Times Cyclic Semi-Solid Heat Treatment

Short times (5 min. / cycle) cyclic semi-solid heat treating process up to four cycles for 6061 aluminum alloy was studied. The microstructures of as-received and cyclic semi-solid heat treatment at the edge of samples at 630 degrees C for one to four cycles were investigated. Short time cyclic heat treatment up to two cycles improves the microstructure to be finer and more globular compared with as-received one. Short time cyclic heat treatment significantly affects the microstructure at the edge of samples only due to short time heating. Optimum values of grain size and grain sphericity at the edge of samples for short cyclic heating time (5 min./cycle) of about 160 mu m and 0.57 respectively. Increasing the number of heat treatment cycles above three increases both shrinkage porosity and micro-cracks formation.