Comprehensive Optimization Of Microstucture And Mechanical Properties In ZL114A Alloy

ZL114A alloy is widely used in the Aeronautic and space fields and so on,which is a high strength and toughness casting Al-Si Alloy.With the development of science and technology,the products of aerospace have more and more high requests to the ZL114A alloy.The tensile strength and elongation of ZL114A alloy sand casting are required more than 320MPa and 4% respectively, while the tensile strength and elongation of ZL114A alloy sand castings are less than 300MPa and 3% respectively in our aviation enterprise.It cannot meet the needs of the Aeronautic and space fields.In this paper, the ZL114A alloy was researched. The effect of the refinement, modification, component optimization and alloying on the microstructure and mechanical properties of ZL114A alloy has been investigated.In order to meet the need of the aeronautical and astronautic fields, the microstrucre would be perfected, and the mechanical properties would be improved.The research results show:Sr has well modification effect on ZL114A alloy's eutectic silicon.As-cast,with the increasing of adding amount of Sr in the alloy, needle shape of Si began thinning, and precipitated along the ? (Al) grain boundary with the small fibrous shape.After T6 treatment,Eutectic Si gradually convert to irregular granular and diffusely distributed in the grain boundary.Research found that:alloy's mechanical properties were increased with adding Sr,and reached the maximum when the Sr content was 0.04% and were depressed then. Adding too much Sr can produce the excessive modification phenomenon and reduced the alloy mechanical properties . Sr-RE compound modification can improve the phenomenon of much pinhole after Sr modification.With the increasing addition of RE,alloy's mechanical properties were improved.When joined RE0.2 %,the mechanical properties reached the maximum,but they were decreased with RE amound increasing then.The H content and the amound of pinhole in the alloy were significantly reduced and alloy castings mechanical properties wre improved by the method of C2Cl6 and argon compound refinement.C2Cl6 refinement was before the Sr modification and argon refinement was after the Sr modification.Ce as a long-term modification agent,which has a very good modification effect on ZL114A alloy.With the increasing amount of Ce,the mechanical properties of alloy was improved.When the Ce amound was 0.2%,the mechanical properties reached the maximum,but they were decreased with Ce amound increasing then.The compound modification agent of Sb-Te has a good modification effect on Si,and also is a kind of long-term modification agent.The mechanical properties of ZL114A alloy were increased firstly and were decresed then with Sb and Te increasing amound.When adding Sb0.3%,Te0.2 %,the mechanical properties of ZL114A alloy were best.The tensile strength was 322.99 MPa and the elongation was 4.65%.Be and Ti are important elements in the ZL114A alloy,because Be can reduce the loss of Mg and Ti can refine the grains.The mechanical properties were improved firstly with the increasing amound of Be and Ti and reached the maximum when Be was 0.04% and Ti was 0.14%.But the excessive amound of Be and Ti made grain coarsening and reducd the alloy's mechanical properties.The mechanics properties of ZL114A alloy were effectively improved by alloying.The alloy's tensile strength was increased firstly and decreased then,but the elongation was decreased always when ZL114A alloy joined with Cu element.When adding 0.1% Cu, the tensile strength was 331.69MPa and the elongation was 3.8%.When adding 0.5% Cu,the tensile strength was 337.21MPa and the elongation was 3.4%.When the Cu addition was more than 0.5%,the tensile strength began to drop and the elongation continued to decline.Compositive considering the alloy tensile strength and elongation, the quantity of Cu alloying should be added 0.1%.The master alloy of Al-5Ti-B is one kind of good grain refinement.The grains of ZL114A were refined and the mechanical properties were increased with the increasing amound of Al-5Ti-B.The mechanical properties began to decrease when adding Al-5Ti-B more than1.0%.Adding Sc and Zr element in the ZL114A alloy which was refined by Al-5Ti-B master alloy would make coarse grains and reduce the alloy mechanical properties.After above study,the compositive optimization scheme for ZL114A alloy was following: alloy component ratio for 7%Si,0.6%Mg,0.14%Ti,0.04%Be;added compound modification agent of 0.04%Sr and RE0.2 %;adopted C2Cl6 and argon combined refinment process;added 1.0% Al–5Ti-B grain refinement agent to refine grains, added 0.1%Cu for alloying process.After optimization scheme,the tensile strength of the ZL114A alloy sand castings by T6 treatment achieved 320MPa and the elongation was more than 4%,and the fracture was ductile fracture.It can meet the aviation and spaceflight enterprises'requirement for sand castings of ZL114A.