Study On A356Aluminum Alloy’s Rifinement And Modification By Adding Composite RE

This paper has studied on the refinement and modification of La-Ce compoundby density measurement, ICP, metallographic observation, mechanical tensile test,SEM and EDS. And the influence on A356’s intergranular corrosion by differentaddition of compound RE was also studied.The results showed that, with composited addition of La and Ce in A356, the averagelength of SDAS and eutectic silicon, contents of Fe and porosity were all reduced; thedensity of cast was obviously improved. La and Ce mutually promoted the refining effect.The cast after refinement and metamorphic at addition of0.1La0.5Ce meeted nationalpinhole standard level1with a density of2.61g/cm3, and its residual iron content wasreduced to only759mg/kg，24.1%lower than that without refinement and metamorphic;its average length of SDAS and eutectic silicon were15.19μm and less than10μm，respectively24.7%and61.8%lower than the cast without refinement and metamorphic.The effects of modification by La and Ce on A356cast’s tensile strength promotedeach other. After modification by only0.1La0.5Ce, F state casting reached the maximumtensile strength of163.9MPa and elongation rate of4.88%; T5state casting reached230.7MPa and5.84%, greatly higher than casting without modification. Throughexperimental verification，0.1La0.5Ce owned a better effection as the secondary refiningagent and modificator, and the F and T5state casting respectively reached the tensilestrength of181MPa and270MPa, but elongation did not change significantly.The modification by composited La and Ce could reduce A356casting’sintergranular corrosion rate, but the excess addition of La would exacerbateintergranular corrosion rate, so the addition of La should be controlled in0.3%. Morethan0.3%addition of Ce could significantly reduce the intergranular corrosion depthand rate. After modification by0.1La0.5Ce compound, A356casting meted nationalintergranular corrosion level2with the maximum corrosion depth of11.58μm，best inintergranular corrosion test, and its weight loss rate0.5582×10-4g/(cm2h) was nearlyone-third of the weight loss rate of the casting without modification.