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Effect of Cr on Microstructure and Mechanical Properties of Al–3.2Mg Alloys

Effect of Cr element on microstructure of Al-3.2Mg alloys was investigated using optical microscopy, scanning electron microscopy (SEM) and EDS. Moreover, the tensile and hardness test were carried out. The results show that a minor additive of Cr can refine effectively the secondary dendrite arm spacing and decrease the number of coarse interdendritic structures. In the whole series of the alloys, the secondary dendrite arm spacing of Al–3.2Mg-0.1Cr alloy was the smallest, and the spacing presented an increasing trend with the Cr content. With high levels of Cr, the intermetallic compounds are formed by Cr with Al, Mg and Fe, the shape of the second phase particles were transformed from bulky bone shape to fine bone shape and long striped. The strength and the hardness of Al–3.2Mg alloys were greatly improved when the additions of Cr were 0.05% and 0.1%, but the ductility of the alloys remained at a low level by adding 0.05%Cr. Therefore, combining with the comprehensive properties and the microstructure, the best addition of Cr in the alloy was 0.10% in the whole series.