| Al-Si-Cu cast aluminum alloy is one of the typical lightweight corrosion-resistant and easy-to-form metal structural materials,and has a wide range of applications in the fields of automobiles,aerospace and other fields.However,there is still a certain gap between the traditional cast aluminum alloy and the performance requirements of some key components in terms of strength and plasticity.(Micro)alloying and strengthening and toughening heat treatment are effective means to improve the microstructure and properties of cast aluminum alloys.Based on the literature review,the work and results obtained in this paper are as follows:(1)The regulation of rare earth elements RE(Ce,Er,Y)on the as-cast microstructure and properties of Al-5Si-5.3Cu-Sr-Zr-Ti cast aluminum alloy was studied.The results show that compared with the addition of 0.2 wt.%Ce and 0.2 wt.%Er,the alloy with 0.2 wt.%Y element has the best modification effect and the best as-cast alloy performance.At this time,the tensile strength is 216.5MPa,the elongation after fracture is 6.46%,and the maximum depth of intergranular corrosion is 50.13μm;the silicon phase is granular,the size is in the range of 1-5μm,and the distribution is uniform;theα(Al)grains are obvious Refinement,size in the range of 45-70μm,and equiaxed dendrites.XRD analysis shows that the three as-cast alloys are all strengthened by dislocation,and the dislocation strengthening degree(σ_ρ)is 61.54-85.90MPa.(2)The regulation of solid solution regime on the microstructure and properties of Al-5Si-5.3Cu-Sr-Zr-Ti-0.2Y cast aluminum alloy in aging state was studied.The results show that the optimal solution regime is 470℃×2h+480℃×2h+490℃×2h+500℃×2h+510℃×16h room temperature water quenching.At T6(191℃×18h)aging state,the tensile strength of the alloy is351.2MPa,the elongation after fracture is 5.38%,and the maximum depth of intergranular corrosion is 115.83μm;Within the range of 10μm,it is uniformly distributed at the grain boundaries of the aluminum matrix.XRD analysis shows that all three solid solution regimes can improve the dislocation strengthening degree of the alloy.TEM analysis shows that the aging precipitation phase of the alloy is GP region+θ’phase;the size of the GP region is about 10 nm,the length of theθ’phase is about 300 nm,and the size of the grain boundary precipitates(GBPs)is about 100×300 nm.Continuous distribution,the width of no precipitation zone(PFZ)is about200nm,the interface between the silicon phase andα(Al)is relatively smooth,and there is no precipitation phase.(3)The regulation of Mg content and solution system on the aging microstructure and properties of Al-5Si-5.3Cu-Sr-Zr-Ti-0.2Y-x Mg cast aluminum alloys was studied.The results show that among the alloys with three Mg contents of 0.38 wt.%,0.88 wt.%and 1.52 wt.%,0.88wt.%Mg has the best microstructure and properties.The optimal solution system is470℃×2h+480℃×2h+490℃×2h+500℃×2h+510℃×16h room temperature quenching.In the aging state at T6(191℃×18h),the tensile strength is 364.4MPa,the elongation after fracture is4.87%,and the maximum depth of intergranular corrosion is 60.71μm;Mg element can reduce the size of the undissolved phase.XRD analysis shows that the increase of Mg content and the prolongation of holding time in the solution system can improve the dislocation strengthening degree of the alloy.TEM analysis shows that the aging precipitation phase of the alloy is GP region+θ’phase+Q’phase;in the two Mg contents of 0.38 wt.%and 0.88 wt.%,when the Mg content in the alloy is 0.88 wt.The size of the inner precipitation is the smallest,the size of the GP region is about 5 nm,the length of theθ’phase is about 30 nm,the length of the Q’phase is about 20 nm,the size of the GBPs is about 40×200 nm,and the distribution is discontinuous,and the width of the PFZ is about 150 nm.The overall performance is the highest.When the Mg content in the alloy is 0.38 wt.%,the size of the GP region is about 5 nm,the size of theθ’phase is about 40 nm,the length of the Q’phase is about 30 nm,and the size of the GBPs is about 50×280 nm,showing a continuous distribution,and the width of the PFZ is about 50 nm.About 150nm,consistent with the decrease in strength and resistance to intergranular corrosion.(4)Design the control arm casting mold and complete the Angcasting casting process simulation,and finally prepare the control arm of this alloy composition.In summary,the rare earth element Y can effectively refineα(Al)and transform the silicon phase,and Mg alloying(the optimum content is 0.88 wt.%)can refine the intragranular precipitation phase.Successfully developed Sr,Zr,Ti,Y quaternary composite microalloyed Al-Si-Cu(-Mg)cast aluminum alloy with high strength,high plasticity and high corrosion resistance The relevant composition design,microstructure characteristics,melting and casting technology,strengthening and toughening heat treatment technology and key process parameters provide a theoretical basis for the subsequent research and development of better high-performance cast aluminum alloys. |
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