Study On Microstructure And Hot Deformation Behavior Of Al-Mg-Si-RE Alloy

In recent years,with the introduction of the national carbon neutral slogan,reducing CO₂emissions has become the focus of social attention.As a lightweight alloy,aluminum alloy has good comprehensive performance and great potential,which has great significance for the country’s energy conservation and emission reduction.At the same time,the country’s requirements for the comprehensive properties of aluminum alloys are gradually increasing.Based on the theory that rare earth elements can improve the comprehensive properties of aluminum alloys.In this paper,Al-Mg-Si-Ce and Al-Mg-Si-Y series alloys are designed based on 6000 series aluminum alloys.In this paper,the effects of Y and Ce elements on the microstructure,mechanical properties and high temperature compressive properties of Al-Mg-Si alloys are mainly studied.（1）In terms of microstructure,the effects of Ce and Y additions on the as-cast structure of Al-Mg-Si alloys were studied.The results show that the addition of Ce and Y can effectively reduce the as-cast grain size of the alloys.When the addition amount reaches 0.15 wt.%the grain size of the alloy is 108.98μm,and the refining effect is the best.At the same time,the addition of Ce can also improve the uniformity of the as-cast structure of the aluminum alloy.And both Ce and Y will form a second phase with Si element in the alloy and precipitate at the grain boundary.The main second phase is approximately AlSiCe and AlSiY phase.At the same time,Ce can also play a role in hindering the growth of grains in addition to refining the grains.（2）In terms of strength,comparing the properties of the alloy,it is found that a small amount of Ce and Y elements can improve the strength of the alloy.However,with the further increase of Y content,the second phase at the grain boundary of the alloy becomes coarse.The Al-Mg-Si-0.15Ce alloy has a peak aging time of 7 hours and a peak hardness of 113.73 HV.The yield strength of the alloy in the peak aging state reaches 260 MPa,the tensile strength reaches 282 MPa,and the elongation after fracture reaches 16%.Compared with the Al-Mg-Si alloy,its yield strength,tensile strength and elongation after fracture are increased by 19%,12%,and 13%,respectively.The yield and tensile strength of Al-Mg-Si alloy with 0.1 wt.%Y content are 263 MPa and 294 MPa,respectively,and the elongation after fracture reaches 14.2%.With the further increase of Y content,the strength of the alloy decreases significantly with the increase of Y content.When the content of Y reaches 0.5wt.%,the yield strength of the Al-Mg-Si-0.5Y alloy is only 232 MPa,resulting in a significant decrease.（3）In terms of hot compression performance,the high temperature compression test was carried out on the homogenized alloy.By analyzing the compression curves of AC0 and AC15alloys,it is found that the addition of 0.15 wt.%Ce reduces the maximum flow stress of the alloys and the activation energy of the alloys has little effect.Which shows that the addition of a small amount of Ce does not significantly improve the deformation difficulty of the alloy.At the same time,the high temperature compression deformation mechanism of AY1,AY2 and AY5 alloys is also analyzed.The results show that with the increase of Y content,the activation energy and the maximum flow stress all showed an increase first and then decrease.The deformation mechanisms of the alloy at 300-450℃and strain rate of 7×10^-2-7×10^-4S^-1 are dislocation slip and climb.