| Al-Cu alloys are favored by aerospace,automotive and petrochemical industries for their high strength,toughness and light weight.However Al-Cu the solidification temperature range of the alloy is large,it is easy to produce thermal cracking,the casting performance is poor,and the corrosion resistance is not good.Therefore,the composition,melting and forming of alloys have always been the focus of domestic and foreign scholars and factories.Taking Al-5.0Cu-XSi-0.8Mn alloy as the research object,the influence of Si elements on casting properties,mechanical properties and microstructure was investigated when the Si content changed in the range of 0.2 wt.%-3.0wt.%.The main conclusions are as follows:using Pandat software to calculate the alloy composition,optimize the process of alloy purification and cast the specific testing mould.(1)When the Si content increased from 0.2 wt.%to 1.0 wt.%,the fluidity of the alloy decreased slightly,and then gradually increased with the increase of Si content,reaching 597.0 mm.at 3.0 wt.%content Si content affects the fluidity of the alloy mainly by changing the viscosity,solidification temperature interval,heat release during solidification surface energy and so on,in which the solidification temperature interval contributes the most.(2)The thermal cracking sensitivity of the alloy is gradually improved with the increase of Si content.the HTS of the alloy decreased from 92 to 28 with increasing Si content.near(f s)1/2=1,the increase of the Si content makes the |ΔT/Δ(f s)1/2| value of the alloy gradually decrease,which leads to the gradual increase of grain growth rate,the faster bonding between grains,and the tendency of the alloy to produce thermal cracks.at the same time,the backfill channel of the alloy liquid becomes shorter and the liquid backfill becomes easier,and finally the HTS of the alloy is reduced by the combination of the two.(3)The addition of the Si makes the plasticity of the alloy gradually worse,and the UTS of the alloy does not change obviously when the Si content is less than 2.0 wt.%,and then with the increase of Si content slightly increased.The use of filter device can effectively reduce the flow rate when the alloy is filled,and then reduce the casting defects of the alloy,the plasticity of the alloy is obviously improved,the effect is more obvious when the Si content is low,and the UTS of the alloy is also improved.(4)The increase in the Si content increases the size of the hole defects in the Al-5.0Cu-XSi-0.8Mn alloys,and there are more Fe-Mn-rich phases in the vicinity of these pores.The fracture of the alloy occurs at these pores,especially on the hard brittle Fe-Mn-rich phase near the pores,and then along the lamellar Al-Si eutectic structure around them.as the Si content increases,the macroscopic fracture surface of the alloy gradually becomes flat and the plasticity gradually becomes poor. |
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