The Effect Of Alloying Elements On The Microstructure And Mechanical Property Of Al-Si-Cu-Mg Cast Alloy

Al-Si-Cu-Mg cast alloy is extensively used mainly because of its good castability and excellent mechanical properties by heat-treatment. The influence of the alloying elements of Zn, Cr, Zr on the mechanical properties and microstructure was investigated in this paper. The strengthening mechanism is also carefully analyzed.Zn, Cr or Zr was added respectively and their influences on the microstructure and mechanical properties were examined. The addition of Zn gives a rise to a newly grained phase containing Cu, Mg, Al. The precipitation of Zn-rich phase is a nucleation site for the θ". θ" phase is even a good consolidation phase for the alloy. Cr combines with Mn, Fe and forms some disperse phases which substitute for other adverse iron-rich phases. The compounds decrease the harmful influence of Fe phases and precipitates dispersely well. The addition of Zr combines with Al and froms β'(Al₃Zr). The β'(Al₃Zr) is a good strengthening phase.The main influence of Zn, Cr, Zr on heat treatment process is that Zn can solute easily in the a (Al) and Zn-rich phase can become nucleation site of θ"and induces formation of θ". It precipates at the grain boundary and retards the formation of θ'. The element of Cr combines with Fe, Cu and forms some new phases in as-cast condition. It can solute in the solid solution. The new phases become the nucleation site of the θ "and accelerate the formation of θ ".The phases containing can even precipate at the grain boundary and restards θ' to precipates at the grain boundary. The addition of 0.20%Zr can solute in the a (Al) in the as-cast sample. The excessive addition of Zr can not solute in the a (Al) in the solid solution stage. The β(Al₃Zr) can become the nucleation site of θ"and accelerate the formation of 9". It even easily combines with the spare space in the grain boundary and postpone the formation of θ'.