The effects of Cr and Zr addition on the microstructure and mechanical properties of rapidly solidified Al-20Si-5Fe alloys

The effects of Cr and Zr addition on mechanical properties of Al-20Si-5Fe alloys, manufactured by gas atomization followed by degassing and hot extrusion, were studied by a combination of scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray microanalysis, X-ray diffractometry, tensile testing and wear testing. The microstructure of extruded bars showed a homogeneous distribution of two different sizes of monoclinic β-Al5FeSi and Si particles embedded in an α-Al matrix. Tensile strengths of Al-20Si-5Fe-2Cr and Al-20Si-5Fe-2Zr alloys at room temperature were 375 and 387 MPa, respectively, which were about 12% higher than that of the Al-20Si-5Fe alloy. However, the effects of Cr or Zr addition on the wear resistance were not significant. Coefficients of thermal expansion of Al-20Si-5Fe-2Cr and Al-20Si-5Fe-2Zr were 16.6 × 10−6 and 17.5 × 10−6 K−1, respectively, which are smaller than that of the Al-20Si alloy.