Study On Preparation、Microstrure And Properties Of Mg-Al-Zn-Si Alloys

Magnesium alloys，characteristic of light-weight，high specific strength and toughness，excellent shock resistance and thermal conductivity，good cutting ability and recyclability，widely used in the fields of aerospace，electronics，automobile，biological and ect.However，the present magnesium alloys have poor high temperature performance，it limits itsapplication. Therefore，it is one of the hot research topic to develop new heat resistantmagnesium alloys and low cost recently.The Mg-x（4，6，8）Al-1Zn-1Si、Mg-x（4，6，8）Al-y（4，6，8）Zn-1Si andMg-4Al-1Zn-z(0.5，1，2)Si alloys were prepared by gravity casting process in this paper.The effects of Al、Zn、Si addition，the alloying with Sb and heat treatment on microstructureand mechanical properties of the Mg-Al-Zn-Si alloys were investigated. The structurerefinement，especially the Mg2Si phase refinement and strengthening mechanisms wereanalyzed. The results are enumerated as follows：（1）The Mg-x（4，6，8）Al-1Zn-1Si alloys compose of-Mg、Mg17Al12and Mg2Siphases. As the increase of Al content, the Mg17Al12phase increase gradually inMg-x（4，6，8）Al-1Zn-1Si alloys. It is found that the Mg2Si phase with Chinese script shapeis very obvious when the Al content is4%and8%in the as-cast alloys. However，when theAl content is6%，the Mg2Si phase with Chinese script shape is not obvious. Therefore, themechanical properties of Mg-6Al-1Zn-1Si alloys are the best. With the increase of Alcontent from4%to8%，the hardness of the experimental alloys increase.（2）Mg-4Al-4Zn-1Si and Mg-6Al-6Zn-1Si alloys mainly compose of-Mg、Mg17Al12、Mg2Si and MgZn phases，but the Mg-8Al-8Zn-1Si alloy consist of-Mg、Mg17Al12、Mg2Si、MgZn and Al2Mg5Zn2phases. Due to the increase of Al and Zn，the Mg17Al12and MgZnphases increase，the tensile mechanical properties of Mg-x(4,6,8)Al-x(4,6,8)Zn-1Si alloysimproved，but the handness reduce.（3）Mg-4Al-1Zn-x(0.5，1，2)Si alloys consist of-Mg、Mg17Al12and Mg2Si phases.As increase of the Si content， the Chinese script shaped Mg2Si phases increased and more obvious gradually in Mg-4Al-1Zn-x(0.5，1，2)Si alloys，the tensile mechanical propertiesof Mg-4Al-1Zn alloys at room temperature reduce，but the tensile mechanical properties atelevated temperatureand hardness increase.（4）The Mg3Sb2phase is formed in Mg-4Al-1Zn-1Si alloy by the addition of Sb. Withthe Sb content increase，the Mg2Si phase is refined in Mg-4Al-1Zn-1Si alloys，above the0.5%Sb，the Mg2Si phases start to aggregate.When the content of Sb is0.5%，the Mg2Siphases change from Chinese script shapes to short pole and block shapes，the mechanicalproperties is in the best.（5）The Mg3Sb2phase is formed in Mg-8Al-1Zn-1Si alloy by the addition of Sb. Whenthe content of Sb is0.8%，the effect of the Mg2Si phases refined is better，meanwhie，themechanical properties in Mg-8Al-1Zn-1Si alloy is in the best. Above the0.5%Sb，thecoarsening Mg2Si appeare and the mechanical properties reduce.（6）Mg-8Al-1Zn-1Si alloy and Mg-8Al-1Zn-1Si-0.6Sb alloy are solution heat-treated at430℃. It is found that the Mg2Si phases are spheroidized gradually and the tensilemechanical properties were improved with the time of solution heat treated increase. Thehardness reduced. The Chinese script shape Mg2Si phases in Mg-8Al-1Zn-1Si-0.6Sb alloy isspheroidized faster than in Mg-8Al-1Zn-1Si alloy.