Nano‐yttrium‐containing precipitates of T6 heat‐treated A356.2 alloy when trace yttrium (Y less than 0.100 wt%) added
Xinping Hu, Qing Wang, Henry Hu, Ruixin Li, Yang Zhao, Zhiming Wang, Bingrong Zhang
Abstract
Abstract To investigate the effect of yttrium (Y) on microstructure refinement and mechanical properties of aluminum alloy A356.2, the different trace contents of Y (0 wt%, 0.025 wt%, 0.050 wt%, 0.075 wt%, or 0.100 wt%) were introduced into the liquid alloy. The alloys were fabricated in a preheated permanent mold, and subsequently treated by a T6 heat treatment. The results of tensile testing indicate that the yield strength (YS), the ultimate tensile strength (UTS) and the elongation (El) of the A356.2 alloy are improved by the Y additions. The YS dependence on grain size for the test alloys follows the Hall–Petch equation, which gives with a correlation of R 2 = 0.83. As 0.050 wt% Y is added, the optimum values of the YS, UTS and El are achieved after T6 heat treatment. The secondary phases were identified by X‐ray diffraction (XRD) which mainly consisted as Si, Mg 2 Si and Al 3 Y. The scanning electron microscope (SEM) and energy‐dispersive spectrometer (EDS) analyses reveal the presence of the nano‐sized Al 3 Y particles on the surface of the Si phase. The A356.2 alloy with the Y addition is strengthened by the dendritic refinement, and the presence of the micron‐ and nano‐sized Al 3 Y precipitates.