Influence of Li(2)Sb Additions on Microstructure and Mechanical Properties of Al-20Mg(2)Si Alloy

It is found that Li(2)Sb compound can act as the nucleus of primary Mg(2)Si during solidification, by which the particle size of primary Mg(2)Si decreased from ~300 to ~15–25 μm. Owing to the synergistic effect of the Li(2)Sb nucleus and adsorption-poisoning of Li atoms, the effect of complex modification of Li-Sb on primary Mg(2)Si was better than that of single modification of Li or Sb. When Li-Sb content increased from 0 to 0.2 and further to 0.5 wt.%, coarse dendrite changed to defective truncated octahedron and finally to perfect truncated octahedral shape. With the addition of Li and Sb, ultimate compression strength (UCS) of Al-20Mg(2)Si alloys increased from ~283 to ~341 MPa and the yield strength (YS) at 0.2% offset increased from ~112 to ~179 MPa while almost no change was seen in the uniform elongation. Our study offers a simple method to control the morphology and size of primary Mg(2)Si, which will inspire developing new Al-Mg-Si alloys with improved mechanical properties.