Effect of silicon and strontium on microstructure and properties of az61 magnesium alloy

Abstract

AZ61 magnesium alloys have been widely used in the transportation industry. Thus, efforts are going to enhance the properties of AZ61 magnesium alloys by minor addition of different elements and applying different treatments. The present study investigated the effects of Si and Sr addition on the properties of AZ61 Mg alloys. AZ61, AZ61-0.8Si, AZ61-1.6Si, AZ61-0.5Sr, AZ61-0.8Si 0.5Sr and AZ61-1.6Si0.5Sr alloy samples were cast, solution treated and hot rolled. Then the samples were aged at 180˚C and 220˚C for different time periods. The transformation of second phase of all six AZ61 alloys are analysed by conducting differential scanning calorimetry (DSC) test. Microstructures were investigated using optical microscope and scanning electron microscope. Microhardness was measured by a Vickers hardness testing machine. It is observed that Si refines the AZ61 Mg alloy during solidification while Sr modifies the Chinese script shape Mg2Si phase of Si added cast AZ61 Mg alloy and decreases the grain size. The major (Mg17Al12) intermetallic of AZ61 alloys formed during casting revealed in DSC analysis are found to be dissolved into the Mg grains and the shape of some undissolved Chinese script Mg2Si phases has been changed after solution treatment. The hardness value increases with increasing aging time at both aging temperatures 180˚C and 220˚Cand maximum hardness is found at the aging time of 19 hours and 16 hours respectively. The maximum hardness among all age hardened six alloys, 1.6% Si addition AZ61 alloy shows the highest maximum hardness. It is also found that the maximum hardness of 0.5%Sr addition in AZ Mg alloy is higher than that of Si addition AZ61 alloy.