Microstructure, mechanical properties and residual stress of high vacuum die casting AlSi10MgMn alloys with different spray quenching

Quenching cooling rate in solution treatment is the decisive parameter for solute supersaturation and mechanical properties after following aging of wrought and casting Al alloys. In this study, the microstructure quantitative characteristics, mechanical properties and residual stress of high vacuum die casting (HVDC) AlSi10MgMn alloys with different cooling rates during spray quenching were comprehensive studied, which were compared with the conditions of air and wind cooling as well as water quenching. The results showed that, with the decrease of quenching cooling rate, the cross-section diameters of the nano-precipitates β" increased, the precipitates number density decreased in the aged alloys, and the precipitate free zone (PFZ) at grain boundary widened. In addition, β' and β phases appeared in the samples quenched by air and wind. As the cooling rate dropped, the ultimate tensile strength (UTS) and yield strength (YS) of as-aged alloys decreased whereas the elongation (EL) increased, and the quenching residual stress declined. A critical quenching cooling rate over 30 °C/s followed with aging treatment was found for strengthening the AlSi10MgMn alloys and reducing quenching residual stress. The results are important for controlling mechanical properties and residual stress in the alloy practical application.