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

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 alpha-dispersoids; however, the best effect was achieved by their combined addition. The optimum heat treatment condition was at 500 degrees C for 8 h; under this condition, the largest quantity of and the finest alpha-dispersoids were obtained, resulting in remarkable improvements in YS at both room and elevated temperatures. The creep resistance at 300 degrees 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 degrees C, doubling of threshold stress and a 50-fold reduction in the minimum creep rate on the creep property at 300 degrees 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 degrees 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.