Microstructure and Microhardness of AlZnMnMg Alloy During Heat Treatment

In this work, the structural changes induced by the chemical nature of alloyed elements and aged treatment showed a beneficial connection with hardness and electrochemical degradation performance. Al-based alloys were investigated by means of the Vickers hardness test, in order to determine the effect of aging treatment on the hardness; X-ray diffraction and scanning electron microscopy were used to identify the phase transformation by the casting and ageing treatment; finally, a short-term electrochemical test to know the electrochemical performance. The results show that the formation of the (MgZn)49Al32 phase occurs under two conditions: when the magnesium content is more than 5.49% in as-cast condition, and the thermal treatment carried out at 450°C for 5 h. In addition, the hardness and electrochemical performance have been influenced by the presence and quantity of the (MgZn)49Al32 phase. The addition of magnesium alloy modifies the microstructure, increases the content of the (MgZn)49Al32 phase, and provides a localized corrosion, which leads to the breakdown of the oxide film (γ-Al2O3) formed on the Al alloy surface.