Microstructure And Properties Of High Strength And Toughness Die Casting Al-Si-Cu Alloy

In recent years,in response to the national carbon peak,carbon neutrality policy requirements,the automotive industry has gradually shifted its focus to automotive lightweight.The automobile body and parts made of traditional steel materials greatly increase the quality of the vehicle,and the use of lightweight aluminum alloy materials instead of steel is an effective method to reduce vehicle weight,improve fuel efficiency and reduce carbon dioxide emissions.At the same time,aluminum alloy die castings produced by die casting molding process have been widely used in the automotive industry.In order to further expand the application range of automobile aluminum alloy die castings,it is of great significance to develop new high strength and high toughness aluminum alloy die castings.In this paper,Al-14Si-4Cu-0.4Mg and ADC12 die-casting alloys were used as the research objects.The microstructure and mechanical properties of high-pressure die-casting aluminum alloys after T5 and T6 treatment were systematically studied by OM,XRD,DSC,SEM and STEM analysis methods and mechanical properties test.In addition,the microstructure and mechanical properties of particle reinforced die-casting aluminum matrix composites were studied.The results show that:（1）There are a lot of dislocation tangles and nano-Si particles in Al-14Si-4Cu-0.4Mg die casting alloy,and most of Cu alloy elements dissolve in aluminum matrix.During T5 aging,the hardness increased first and then decreased,and the electrical conductivity increased gradually.During aging,the hardness and electrical conductivity of the alloy increased due to the formation of GP zone.After overaging,the nano-Al₂Cu phase precipitates,while a large number of dislocation entanglements and nano-Si particles disappear in the alloy microstructure,the hardness decreases slightly,and the conductivity continues to increase.The die casting alloy aged at 175℃for 7 h has the best mechanical properties.and the tensile strength,yield strength and elongation are 293 MPa,212 MPa and 3.1%,which are increased by 21%,22%and 11%compared with the as-cast alloy,respectively.（2）The surface of Al-14Si-4Cu-0.4Mg die casting alloy did not appear obvious foaming phenomenon after short time solid solution treatment.Short time solid solution treatment can make eutectic Si spheroidization and Al₂Cu phase partially dissolved in the matrix.The best solution treatment scheme obtained from the experiment is to keep the temperature at 500℃for 20 min.After aging at 175℃for 7h,the alloy has excellent mechanical properties,and its Brinell hardness can reach153 HB.The tensile strength,yield strength and elongation are 360 MPa,233 MPa and 4.7%,respectively,which are increased by 48%,32%and 68%compared with the as-cast alloy,respectively.（3）ADC12 die casting aluminum alloy microstructure includes coarseα-Al₁and fineα-Al₂;with the increase of Al-5Ti-B master alloy addition,coarseα-Al₁grains and massiveα-Al Fe Mn Si phases are effectively refined.When the addition of Al-5Ti-B reached 5%,α-Al₁was no longer refined,and needle-like coarse Al₃Ti phase appeared in the microstructure.When the addition of Al-5Ti-B is 3%,the hardness and tensile properties of Ti B₂/ADC12 composites are the best,and the average hardness reaches 110 HB.The tensile strength,yield strength and elongation are 290MPa,179 MPa and 6.2%,respectively,which are promoted by 26%,22.6%and34.7%compared with those of the matrix alloy.