Hot Tear Formation During the Casting of Al-Zn Binary Alloys

The hot tearing susceptibility of Al-Zn binary alloys with solute contents of Al-0.5%Zn, Al-1%Zn, Al-2%Zn, and Al-4%Zn, with all compositions being in wt%, is investigated through physical experiments and numerical simulation. The temperature at the hot spot, the designed critical point for hot tearing, and the load at the end of the test bar are measured and compared with the simulation results. The test samples with 0.5 and 1.0% Zn show hot tears while those with 2.0 and 4.0% Zn have no sign of such tearing. The correlation between solid fraction, strain, stress, and hot tearing indicator is revealed using the simulation results of the Al-1%Zn and Al-4%Zn alloys. Just before solidification, the Al-1%Zn alloy is found to have not only a much higher strain rate at the hot spot of the test bar than that of the Al-4%Zn alloy, but also a higher strain gradient along the longitudinal direction. It is believed that both the high strain rate and high strain gradient are attributable to the formation of hot tears in the Al-1%Zn alloy. Most of the solidification of the Al-1%Zn is concentrated in a narrower band at the center of the test bar with a higher rate of solidification. The formation of hot tears in the Al-1%Zn alloy is caused by the low permeability, high strain rate, and high strain gradient generated in the last moment of solidification.image (c) 2023 WILEY-VCH GmbH