Effects of Quenching Cooling Rate on Residual Stress and Mechanical Properties of a Rare-Earth Wrought Magnesium Alloy

Abstract

To investigate the effect of quenching rate on microstructure, residual stress (RS) and mechanical properties of a rare-earth wrought magnesium alloy Mg-Gd-Y-Zr-Ag-Er, RS in 20 °C water quenching (WQ (20 °C)), 100 °C water quenching (WQ (100 °C)) or air cooling (AC) conditions were measured and compared with the simulation results, corresponding mechanical properties and microstructure in quenching and aging state were studied. The decrease of quenching rate has little effect on the grain size but makes the twinning disappear, precipitates increase and the texture weakened, leading to easier brittle fracture after aging. WQ (100 °C) is the best quenching condition in this study, with a significant decline in RS and only 4.9% and 3.7% decrease in yield stress (YS) and hardness compared with WQ (20 °C). The results make it feasible to invent an appropriate quenching method of greatly reducing RS while maintaining mechanical properties. The research conclusions would be beneficial to the application of the alloy.

Study on the Optimization of Heat Transfer Coefficient of a Rare Earth Wrought Magnesium Alloy in Residual Stress Analysis

“…Material parameters of density, thermal conductivity, expansion coefficient, Yong's modulus, Poisson's ratio, etc. at different temperatures were tested, respectively, the above measurement and simulation methods are more detailed in the previous research [17]. 4, the general trend of the curves was that the temperature drops quickly at first and then slowly, and almost flat within 200 s, which was consistent with the decrease in temperature difference between the sample and water.…”

“…The alloy was melted and cast above 700 • C and was die forging at ~460 • C, then immersed into 20 • C water within ~60 s to prevent grain growth. The mechanical properties can be referred to the previous research [17].…”

“…Material parameters of density, thermal conductivity, expansion coefficient, Yong's modulus, Poisson's ratio, etc. at different temperatures were tested, respectively, the above measurement and simulation methods are more detailed in the previous research [17]. conditions above.…”

“…This is because the difference between the quenched and aged states mainly lies in the precipitation strengthening, but the precipitated phase in this alloy is relatively small in quantity compared with the magnesium base. Although the elastic modulus is very much related to the RS [30], previous studies [17] have shown that the elastic modulus of the quenched To further explain the accuracy of the optimized HTC for RS simulation, AARE was applied to quantify the deviation between the measurement and the simulation value of the two models above, as shown in Table 4. The values in the circumferential and axial direction of the IHTM are 22.13% and 17.38%, respectively, which could be acceptable in engineering applications, while the corresponding values are 55.33% and 24.71% in the ILCM.…”

“…The heat transfer model is usually used to simulate the temperature value in heat treatment, Jia et al [14] and Le et al [15] used the heat transfer model to simulate the air-cooling transport process of the AZ31B plate whose average HTC was 20 W/(m 2 • • C). Furthermore, the coupled temperature-displacement model is widely applied in RS analysis [16,17], the intense heat exchange brings uneven deformation inside and outside the material which induces RS.…”