Evolution of dispersoids and their effects on elevated-temperature strength and creep resistance in Al-Si-Cu 319 cast alloys with Mn and Mo additions

Abstract

The present work investigated the evolution of dispersoids during various heat treatments via Mn and Mo additions and studied their effects on the yield strength (YS) and creep resistance at elevated temperature in Al-Si-Cu 319 cast alloys. The results showed that the individual addition of Mn or Mo promoted the precipitation of α-dispersoids; however, the best effect was achieved by their combined addition. The optimum heat treatment condition was at 500 °C for 8 h; under this condition, the largest quantity of and the finest α-dispersoids were obtained, resulting in remarkable improvements in YS at both room and elevated temperatures. The creep resistance at 300 °C was enhanced owing to the additions of Mn and Mo. Compared with the properties of the base alloy, a 19% improvement in YS at 300 °C, doubling of threshold stress and a 50-fold reduction in the minimum creep rate on the creep property at 300 °C were achieved by the combined addition of Mn and Mo. The alloy with both Mn and Mo exhibited the lowest YS decline rate and no change in the minimum creep rate during prolonged thermal exposure at 300 °C for up to 1000 h, demonstrating the superior thermal stability achieved by the 319 alloys with the introduction of a sufficient number of dispersoids from Mn and Mo additions.