The Influence Of Modification On Mechanical Properties Of ZL101Alloy

In order to develop a new engine material for diesel engine head, modification and heat treatment for ZL101were investigated in systematic way and as a basis for tensile and hardness mechanical properties test. The effects of Sr modification on the microstructure and mechanical properties of ZL101alloy were studied by the addition Al-Sr master alloy. The effects solution treatment was investigated by using different heat treatment technic. The optimum composition was determined above study.The spheroidization of eutectic phase during solution treatment was accelerated by Sr modification and a-Al dendrites was also refinement. The modification effect of Sr was significantly when the Sr adding amount between0.02%and0.06%. With Sr amount continued to increase, the eutectic silicon in the aluminum alloy would re-grow up. The holding time had huge influence on morphology of crystal silicon in ZL101alloy, when holding time was30minutes, the effect of modification was best. But if extended the holding time to3hours, the eutectic silicon in alloy would re-grow up. Through the analysis of metallographic microstructure and production cost consideration, determined the best modification process of ZL101was the addition amount of Sr was0.02%, the holding time was30minutes.In the same solid solution heat preservation temperature, extended holding time, the needle-like eutectic silicon phase will change into the roundness, but this changing time was long. The addition of Sr will accelerate the eutectic silicon particles morphology change process and make this progress more smoothly, thus improving the mechanical properties of alloy. But if the solid solution heat preservation time is too long, eutectic silicon particles will gather to grow up, the mechanical properties of alloy will drop. When the addition amount of Sr is0.02%, choose535℃as the solid solution heat preservation and hold the temperature6hours and200℃as the aging treatment and hold the temperature5hours, the mechanical properties of alloy will reach the best. Among them the tensile strength and elongation ratio and yield strength were242.8MPa,3.8%,196MPa. But without the modification of Sr, the mechanical properties will drop obvious.Through the tensile fracture by scanning electron microscopy shown that the fracture without modification of Sr was brittle fracture. The fracture with modification of Sr was ductile fracture and lots of dimples could be seen in the fracture morphology. The longisection of tensile fracture shown that the crack initiation near the eutectic silicon particles. Without modification treatment, the crack in ZL101alloy propagated the combination face between the eutectic silicon particles and matrix, the fracture was wear crystal fracture. With the modification of Sr, the crack in ZL101alloy extended around tiny eutectic silicon particles, the fracture mode was intergranular fracture.