In the present work, Mo was added to an Al–Si–Mg foundry alloy to study its influence on the evolution of dispersoids during various heat treatments. The microhardness and the elevated-temperature tensile properties and creep resistance were measured to evaluate the contribution of dispersoids. Results showed that the addition of Mo greatly promoted the formation of α-dispersoids. During solution treatment, the formation of α-dispersoids started after 8 h at 500 °C. At high temperature (540 °C), the coarsening of dispersoids with increasing time became predominant. The optimum condition of dispersoids can be reached by 520 °C/12 h or 500 °C/4 h + 540 °C/2 h, leading to the highest differences in microhardness between the Mo-containing alloy and base alloy. The tensile strengths were improved at both room temperature and elevated temperatures, while the elongation at elevated temperature was greatly increased. The creep resistance at elevated temperature is further enhanced due to the Mo addition.

Eutectic Al–13% Si alloys are widely used in automotive components, such as pistons and cylinder heads. Recently, the demand on the performance of piston alloys at high temperature is greatly increased to enhance the engine efficiency and to reduce exhaust emission. In the present work, Mn was added to strengthen the aluminum matrix via the formation of thermally stable dispersoids. The evolution of dispersoids during heat treatment and their influence on elevated-temperature properties were studied. The results showed that the as-cast microstructures in the experimental alloys without/with Mn addition were similar, which were composed of eutectic Si, primary Mg2Si, Al–Fe–Ni, Al–Cu–Ni, and π-Al–Mg–Fe–Si intermetallic phases. In the alloy with Mn addition, a number of α-Al(Mn,Fe)Si dispersoids started to form after a heat treatment at 425 °C for 24 h and reached the peak condition at 500 °C for 6 h, resulting in a remarkable increase of the microhardness at room temperature and the improvement in the yield strength and creep resistance at 300 °C. As a complementary strengthening mechanism, the dispersoid strengthening in the aluminum matrix provides a novel approach to improve the elevated-temperature properties of Al–Si piston alloys.

In the present work, various Mn amounts (up to 2 wt%) have been added into Al–Mn–Mg 3004 alloy to study their effect on the evolution of microstructure and elevated-temperature properties. Results showed that the dominant intermetallics are interdendritical Al6(MnFe) until to 1.5 wt% Mn. With further addition of Mn to 2 wt%, the blocky primary Al6Mn/Al6(MnFe) and high volume of fine Al6(MnFe) intermetallics form in the matrix, leading to the rapid increase on the volume fraction of intermetallics. After the precipitation heat treatment (375 °C/48 h), the precipitation of dispersoids increased with increasing Mn contents and reached the peak condition in the alloy with 1.5 wt% Mn, resulting in the highest yield strength and creep resistance at 300 °C. However, the elevated-temperature properties became worse in the alloy with 2 wt% Mn due to the lowest volume fraction of dispersoids and highest volume of dispersoid free zone.