Effects Of Mn And The Composite Modification Of Sr And Ca On The Microstructure And Properties Of Mg-Al Alloy

In the research of magnesium alloy, alkaline earth element occupies a special status. At present, alkaline earth magnesium alloys research is at a very rapid development situation. All kinds of new alloys and new technologies are commonly reported. Our country is a big country of magnesium resources, so how to research and develop magnesium resources is an urgent task. For a long time, the application of alkaline earth elements is behind developed countries, therefore, it is of great significancey to research and develop magnesium from all aspects. Based on this background, the main content of this paper select Mg-8A1as matrix alloy. Effects of Mn and the composite modification of Sr and Ca on the microstructure and properties of Mg-Al alloy have been investigated by using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) in this study. The results indicate that:(1)With the increasing Mn content, Mg-8A1magnesium alloy is obviously refined, the shape of β-Mg17Al12is from continuous or semi-continuous into small size. Near the boundaries, new phases Al8Mn5can be observed, and the amount of Al8Mn5phase increases. Among the Mn-containing alloys, the alloy with the addition of0.5wt.%, the grain boundary increased and coarsening. The addition of Mn can modify mechanical properties of Mg-8A1magnesium alloy obviously at room temperature. Among the Mn-containing alloys, the alloy with the addition of0.3wt.%Mn exhibits the relatively optimum mechanical properties. Mechanical properties tensile strength and elong reached the maximum147MPa and11.3%, respectively, compared with Mg-8A1alloy increased by11.4%and18.9%. As the Mn content continue increased to0.5%, although the macro-hardness of magnesium alloy has increased, but the tensile strength strength and elongation are greatly decreased. As the Sr content increased, Mg-8Al-xMn magnesium alloy was changed from cleavage fracture to ductile fracture, and then to the cleavage fracture mode.(2)With the increasing1-2%Sr content, new phases Al4Sr can be observed at the grain boundaries. Meanwhile, the shape of β-Mg17Al12is changed. As the Sr content increased, the amount of β-Mg17Al12phase disappears and Al4Sr phase becomes coarse grid. With increasing Sr content, the hardness value of the test alloy first increased, and then decreased. The maximum hardness value is60.5HB with content of1.5%Sr. Among the Sr-containing alloys, the alloy with the addition of1.5wt.%Sr exhibits the relatively optimum mechanical properties, the best tensile properties at room temperature is160MPa, and the elong reached the maximum of15.04%.As the Sr content increased, the fracture mechanism of AM80alloy at room temperature was changed from cleavage fracture to ductile fracture, and then to the cleavage fracture mode.(3)With the increasing Ca content, AM80-1.5Sr magnesium alloy is obviously changed. With the increasing1%Ca content, the shape of β-Mg17Al12phases change from continuous or semi-continuous to small size. As the Ca content increased to1.5%, β-Mg17Al12phase is obviously suppressed, and new particle shape phases Al2Ca can be observed. As Ca content continue increased, the particle shape Al2Ca phase of magnesium alloy almost disappear, and change to the semi-continuous herringbone, and then completely transform into continuous grid. Among the Mn-containing alloys, at room temperature and high temperature the alloy with the addition of2wt.%Ca exhibits the relatively optimum mechanical properties. Hardness and tensile strength reach to57.5HB and145MPa, meanwhile, high temperature tensile strength reach to128MPa. As the Ca content increased, the fracture mechanism of AM80-1.5Sr-xCa alloy at room temperature was changed from cleavage fracture to ductile fracture, and then to the cleavage fracture mode.