Factors affecting thermal contraction behavior of an AA7050 alloy

The understanding of the contraction behavior in high-strength wrought 7XXX-series alloys is very important for the analysis of stress–strain development and modeling of hot tearing and cold cracking in direct-chill casting. The linear thermal contraction during and after solidification of an AA7050 alloy has been studied experimentally under different conditions. The experimental parameters included the sample height (metal level in the mold), grain refining, and gas content. The results showed that evolution of gas during solidification and pressure drop across the mushy zone are the main reasons for the preshrinkage expansion. The measured coefficient of linear thermal contraction decreases with the decreasing grain size at all temperature ranges. The role of gas precipitation and grain refining is discussed.