Effect Of Rare Earth La,ce On Micro/macro-structures And Properties Of Zl101a Alloy

The microstructure and stereo morphology of eutectic silicon were investigated using optical microscopy, SEM with energy spectrometer, DSC, etc. The universal material testing machine was used to test the mechanical property of ZL101A. The main results are described as below:Both La and Ce are good modifiers for ZL101A alloy, which change the eutectic Si morphology from needle-like to short rod-like. The fine modification effect was observed with 0.6%La or 0.8%Ce. The consumption of rare earth can be reduced when modification temperature was increased, but excessively high temperature may worsen modification effect and the proper modification temperature is 760℃for ZL101A alloy. Although La, Ce has fine modification effect after half an hour holding, Ce seems to need more time to obtain the best modification effect and the research show that: Ce has 1h incubation time. Cooling rate has remarkable effect on modification and fine modification can be observed with 0.6%La or 0.8%Ce in metal mould(cooling rate: 5.8℃/s), but no modification was observed in firebrick mould(cooling rate: 0.8℃) at the same adding amount and it seems that the eutectic silicon is more coarse than unmodified state. Rare earth is an excellent refiner and the grain size can be decreased from 3mm (unmodified state) to 1mm.Rare earth and Sr complex modification has better effect than rare modification or Sr modification. The results show that: the consumption of rare earth can be decreased and fine modification can also be available with complex modification (0.015%Sr and 0.2%La). In addition, the incubation time of Sr was shortening by complex modification. Complex modification reduce the temperature sensitivity and the finest modification effect can be available at 720℃. Complex modification has better effect on grain refinement than single rare earth modification or Sr modification and the grain can be decreased to 0.5mm.Both rare earth modification and complex modification have beneficial influence on tensile strength and elongation of ZL101A alloy. The tensile strength was increased from 260.3MPa to 324.5MPa after complex modification by rare earth and Sr. The elongation was also increased remarkably, from 2.3% to 6.0%. It is important to note that the trend for increase of the hardness is not obvious after modification. The growth of eutectic silicon was depressed by rare earth element which mainly enriched at the reentrant of eutectic silicon and interface of aluminum and silicon, and the element enrichment is the key of modification.