Effect of extrusion temperatures on the microstructures, mechanical properties and thermal properties of PM Al-20Si alloy

Abstract

Al-20Si alloy is fabricated by extruding pre-alloyed powder at different temperatures ranging from 350° to 550°C. Morphologies of the Si phase, mechanical properties and thermal properties of the alloy are influenced by extruding temperature. The alloy extruded at 350 °C mainly contains fine eutectic Si. Although its fine structure imparts high strength to the alloy, it is not stable in high-temperature CTE test and tends to agglomerate into large Si lumps due to Oswald ripening effect, therefore offsetting the restriction effect of Si on the thermal expansion of Al and thus increasing the CTE of the alloy. In contrast, the alloy extruded at 550 °C exhibits primary Si phase, which is large in size and more stable in the CTE test. Moreover, it has in-situ formed amorphous/δ * - Al2O3 at the grain boundaries which reduces the CTE of the alloy further. As a result, the alloy fabricated at 550 °C exhibits the best combination of thermal properties (i.e. TC 184.5 Wm−1K−1 and CTE 20.9 ×10−6 K−1 at 400 ℃).