Microstructure And Mechanical Property Of Hypereutectic Al-Si Alloy By Squeeze Casting

As Al-Si alloy has a series of advantages, such as good fluidity and casting property, itis a kind of Al alloy that has most varieties and is most widely used. However, there arealso many defects in Al-Si alloy which seriously affect its comprehensive property, such asneedle eutectic silicon phase, and the thick primary silicon phase. The purpose of thisexperiment is to use squeeze casting process to improve alloy’s microstructure andproperty.In order to research the effect of squeeze casting on microstructure and property ofAl-Si alloy, prepare different Si content Al-Si alloy by squeeze casting. For hypoeutecticAl-Si alloy, solidification under the pressure make original primary-Al dendrites ofhypoeutectic Al-10Si-0.3Mg alloy transform to afterbirth-like crystal, and with the specificpressure increasing, elliptical-Al phase become rounder and smaller. Under598MPa, theproperties of squeeze casting Al-Si alloy is the best, the hardness is66.8HB. Forhypereutectic Al-Si alloy, as specific pressure increasing, bulky and sharp edged primarysilicon phase of hyper-eutectic Al-22%Si alloy became smaller and rounder, and thenumber of Si phases become less; the primary-Al dendrites increase, and become moreand more fine and dense. Under935MPa, the alloy has the best property, the hardness is77.9HB, and compared with gravity casting, it increased by26.8%.At the same time, this test prepare multicomponent hypereutectic Al-Si alloy bysqueeze casting and it was found that solidification under the pressure can not onlyimprove Si phase appearance, but also improve the solid solubility of some strengtheningphase such as Al2Cu phase and Al1.9Cu1.0Mg4.2Si3.3phase, this made the alloy’s propertyfuther improved. Experiment result are that solidification on the pressure of676MPa, thehardness of alloy is107HB and it reached to maximum, after T6heat treatment with525℃(6h)+175℃(10h), the hardness was further improved to150HB.After hot extrusion of squeeze casting Al-Si alloy, the tensile strength and toughnessof alloy are further improved. The billets under290MPa have better mechanical propertiesafter hot extrusion, the tensile strength is177.39MPa, and the elongation is16.24%, obviously higher than the sample before.In order to research the effect of homogenization on the appearance and size of Siphase of alloy, and its abrasive resistance, homogenizing the hypereutectic Al-Si alloy indifferent temperature and time. It can be found that within a range of temperature and time,as the increasing of temperature and the extension of time, the size of Si phase becomebigger and bigger, and the its appearance become rounder and rounder, after homogenizing24h under535℃, the Si circularity is0.76and the diameter is3.57μm. At this time, thealloy have the best abrasive resistance, the attrition rate is4.11×10-3mm3/m. when continueto extend the time, Si phase appearance slightly coarsening, the resistance rate of the alloyis increased.