Study On Microstructures And Properties Of Mg12Al-0.7Si Alloys Modified By Sb And Sr After Equal Channel Angular Pressing

It is well known that magnesium alloy with high alumina content has good room temperature properties, However, it exhibites bad high temperature properties. We can improve the high temperature properties by Si addition, but under the low solidification rates the Mg-Al-Si based alloys easily form the coarse Chinese script shaped Mg2Si phases which would damage the mechanical properties of the alloys (especially for the elongation), So, We use equal-channel angular pressing (ECAP) to modify the size of matrix and the Mg2Si phase, aim to prepare the high-performance magnesium alloy.In this work, we design four kind of magnesium alloy:Mg12Al, Mg12Al-0.7Si, Mg12Al-0.7Si-0.5Sb and Mg12Al-0.7Si-0.09Sr; and then we use Leica DM2500M optical microscope(OM) and JSU-6700F scanning electron microscopy(SEM) to analyse microstructure of initial alloy and ECA pressed alloy, Phase analyses were carried out by X-ray diffractometry, DTA was used to analyze the modification mechanism, the room/high tensile test were carried out by MTS machine, the main findings were:(1) The experimental alloy shows the coarse Chinese script shaped Mg2Si phases which would damage the room temperature mechanical properties of the alloys, reducing from the initial150MPa to121MPa, however, the high temperature mechanical properties increased slightly, from96MPa to101MPa, after4passes ECAP, the Mg12Al-0.7Si alloy show much better mechanical properties than the Mg12Al alloy, which means the morphology and distribution of Mg2Si phase play an important role in the mechanical properties of the alloys.(2) After different passes ECAP, the size of matrix and the second phase decrease remarkably,6passes ECAPed alloy, which has the best microstructure (the matrix size was10μm,β phase was4μm), exhibites the highest room temperature mechanical property,286MPa, the elongation rise to5.1%because of its basal plane (0002) texture when it is8passes pressed;2passes pressed alloy shows the good high temperature mechanical property,204MPa, and the elongation rise to34.4%when it is6passes pressed.(3) The morphology of Mg2Si changed from the coarse Chinese script shaped to polygon block after Sb addition and to the limb-like shaped after Sr addition in the Mg12Al-0.7Si alloy, which means the undercooling control the Mg2Si morphology; the mechanical properties was improved, from121MPa to149MPa (Sb addition) and158MPa (Sr addition).(4) The trend of microstructure and mechanical property of Mg12Al-0.7Si-0.09Sr alloy was consistent with the Mg12Al-0.7Si alloy and they shows better mechanical property than Mg12Al-0.7Si alloy at the same ECAP passes pressed.6passes ECAPed alloy, which has the best microstructure, exhibites the highest room temperature mechanical property,316MPa (increase extent10.5%), the elongation rise to5.48%(increase extent9.3%) because of its basal plane (0002) texture when it is8passes pressed;2passes pressed alloy shows the better high temperature mechanical property,223MPa (increase extent7.4%), and the elongation rise to46.1%(increase extent34%) when it is6passes pressed.According to this, the morphology of Mg2Si changed after Sb and Sr addition, Equal-channel angular pressing (ECAP) makes the matrix refine and the Mg2Si further dispersive comparing the Mg12Al-0.7Si alloy without Sr and Sb addition.