Abstract
Nine kinds of rare-earth free Mg-Al-Sn-Mn magnesium alloys were designed by orthogonal method. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and tension tests were carried out to investigate the microstructures and mechanical properties. As-cast Mg-Al-Sn-Mn alloys have an obvious dendritic structure that is composed of α-Mg, Mg17Al12, and Mg2Sn phases. After hot extrusion, the cast dendrite structure changed into a recrystallized equiaxed grain. Mg17Al12 dissolved completely into a matrix, and only α-Mg, Mg2Sn, and a few Al-Mn phases could be observed. The influence of three alloy elements (Al, Sn, and Mn) on grain size, texture intensity, ultimate tensile strength (UTS), tensile yield strength (TYS), and elongation (EL) were studied by extreme difference analysis method. The content of Mn had the greatest influence on grain size. The AT61-0.2Mn and AT73-0.2Mn alloys had the smallest grain, reaching 6.8 μm. The content of Al had the greatest influence on the strength; therefore, the AT73-0.2Mn alloy had the highest UTS, 322 MPa, and TYS, 202 MPa. The content of Sn had the greatest influence on elongation. The AT52-0.4Mn alloy had the highest elongation in theory, but it was not included in the nine designed kinds of alloys yet. AT52-0.2Mn alloy had the highest elongation in the nine alloys (28.4%).
Highlights
Magnesium alloys are widely used in the automotive field owing to their rich resources, low density, high specific strength, and specific stiffness [1,2,3,4,5,6]
Magnesium alloys have the characteristics of poor deformability, poor corrosion resistance, and low strength compared with Al alloys, which seriously restrict the wide application [7,8,9]
Extrusion can markedly improve the strength by refining the grains [10], and the method has been used to improve the strength of commercial magnesium alloys, rare-earth magnesium alloys, and non-rare-earth magnesium alloys [11,12,13]
Summary
Magnesium alloys are widely used in the automotive field owing to their rich resources, low density, high specific strength, and specific stiffness [1,2,3,4,5,6]. Magnesium alloys have the characteristics of poor deformability, poor corrosion resistance, and low strength compared with Al alloys, which seriously restrict the wide application [7,8,9]. Deformation (extrusion, rolling, and so on) and alloying are important ways to obtain excellent comprehensive properties of magnesium alloys. The addition of rare-earth elements can refine the grain and form the second phase, and a small amount of rare earth (RE) addition can achieve good comprehensive mechanical properties [14,15,16,17].
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