Effects of Al Concentration on Microstructure and Mechanical Properties of Mg-xAl-1Zn-1Si Alloy

The effects of Al content on the microstructure and mechanical properties of alloys Mg-x Al-1Zn-1Si(x=4, 6, 8,wt%) were studied. The results show that the microstructure of as-cast Mg-x Al-1Zn-1Si consists of α-Mg matrix, β-Mg17Al12 phase and Mg2 Si phase. The average grain size of α-Mg matrix decreases first and then increases with increase of Al content. Moreover, the volume fraction of β-Mg17Al12 phase decreases and the coarse Chinese script type Mg2 Si particles becomes fine bacilliform. The average grain size of α-Mg matrix are 30, 20 and 40 μm respectively with the increase of Al content from 4% to 6% and 8%, while the hardness of the alloys increases gradually. The ultimate tensile strength, yield strength and elongation of alloys increases with the increase of Al content from 4% to 6% at room temperature and 150 ℃and then decreases when Al content is 8%. The fracture mechanism of the alloy is quasi-cleavage brittle fracture.