Microstructure, elevated-temperature mechanical properties and creep resistance of dispersoid-strengthened Al-Mn-Mg 3xxx alloys with varying Mg and Si contents

In the present work, the effects of magnesium and silicon addition on microstructure, elevated-temperature yield strength and creep resistance of Al-Mn-Mg 3xxx alloys were investigated. The microstructure evolution under as-cast and heat-treated conditions was quantitatively evaluated by optical and electron microscopy. Results revealed that both magnesium and silicon had an important influence on the distribution and volume fraction of precipitated dispersoids in 3xxx alloys. Without Mg or Si addition, dispersoids could hardly form during the precipitation heat treatment; hence, the alloys free of Mg or Si possessed low yield strength and creep resistance at elevated temperature. A significant improvement in elevated-temperature yield strength and creep resistance was obtained over a wide range of Mg (0.5-1.5 wt%) and Si (0.25-1 wt%) content studied due to the precipitation of a large number of dispersoids. The best combination of yield strength and creep resistance at 300 ℃ was obtained by the alloy containing 1.0 wt% Mg and 0.25 wt% Si with the maximum volume fraction of dispersoids and the minimum volume fraction of dispersoid free zone. The effects of dispersoid strengthening, solid solution strengthening and grain size on yield strength and creep resistance were discussed based on experimental results.