Study Of Microstructure And Properties On New Microalloyed Aluminum Alloy Used For Automotive Sheet

As the preferred material for automotive lightweight,aluminum has many excelle-nt properties,such as light density,high specific strength,good impact resistance,form-ing and recycling process more convenient.In order to promote the development of transformation for lightweight and environmentally friendly automotive,aluminum alloy in application of automotive body panel has become an inevitable trend.AI-Mg-Si-Cu alloy,based on the chemical compositions of AA6010 alloy,were designned to five different alloy compositions.Al-Mg-Si-Cu alloy were prepared by liquid casting,hot extrusion and asynchronous hot-rolling.The chemical and phase compositions were detected by plasma atomic emission spectrometry(ICP),energy dispersive spectrometer(EDS)and X-ray diffraction analysis(XRD).The microstructure and fracture morph-ology were observed by optical microscope(OM)and scanning electron microscopy(SEM).Electron backscatter diffraction(EBSD)was used for grain analysis and texture studies.The main phases of as-cast Al-Mg-Si-Cu alloy include Ali.9CuMg4.1Si3.3,Mg2Si,a-Al9Fe0.84Mn2.i6Si,?-Al9Fe2Si2,Si,and so on.The rare earth phase were precipitated after added Ce and Er.AI-Mg-Si-Cu alloy were homogenization annealed at 520 ? for 12h.The ?-Al9Fe2Si2 phase was not completely converted to a-Al9Fe0.84Mn2.i6Si phase.Mg2Si,Al1.9CuMg4.iSi3.3 and(a-AI+Mg2Si+Si)eutectic were not found because of resolving,and the needle-like or granular particles were evenly precipitate.Change in Vickers hardness of as-cast and annealed Al-Mg-Si-Cu alloy was consistent trend,but hardness of annealed alloy was significantly reduced.As-cast organization was broken during hot extrusion and distributed along the extrusion line.Microstructure characteristics of Al-Mg-Si-Cu alloy were a strip-like structure.During hot extrusion,the dynamic recrystallization was occurred,and the grains were distributed in the gap of deformed grains.The result of ODF maps show deformed texture mainly contains Brass,S and {111}//ND,recrystallization texture mainly contain Cube,Goss and P.The Cu was favorable for evolution of {011}//ND texture and the formation of Cube texture.There was increment in strength and decree-ment in plasticity with increasing the Cu contents.When Ti and Zr were added,the strip structure was effectively refined.P and F textures were strengthened,Cube texture was significantly inhibited.Therefore,the yield strength of alloy was significantly increased.When Ce and Er were added,the striped structure has disappeared.Brass texture trans-form into P texture was inhibited,and formed a stronger Goss texture.The compre-hensive performance of alloy was better.The fracture morphology of the hot-extruded Al-Mg-Si-Cu alloy exhibited typical dimple fracture pattern and a good plastic deformability.After asynchronous hot-rolling,microstructure of Al-Mg-Si-Cu alloy was elong-ated and distributed along rolling direction.The sub-structure,which inside of band-like structure,was along the rolling direction of 45°.The dynamic recrystallization grains are distributed in the band gap.Al-Mg-Si-Cu alloy was solution treatment at 580 ? for 1h,artificial aged at 180?.After then,microstructure was mainly composed of flatten-ed crystallization grain.With rolling temperature or reduction increased,the phenolme-non of recrystallization was more obvious.Best rolling process was the temperature and reduction reached 450? and 75%,respectively.The grain structure of AA6010-0.4%Cu alloy was the most refined and uniform,The UTS(ultimate tensile strength)and elonga-tion were 400MPa and 18%,respectively.The fracture surface was lamellar or dimple,still was plastic fracture.In early artificial aging(180?),hardness of Al-Mg-Si-Cu alloy increased rapidly,the aging peak time was about 3h.Aging peak hardness increased with the increasing of Cu content,and it was further improved when Zr and Ti addition.The aging process was significantly accelerated by added Ce and Er,the aging peak time was reduced to 1h,but aging peak hardness was slightly lower.The strength increased with the incre-asing of Cu content,when Al-Mg-Si-Cu alloy reached the aging peak.The YS(yield strength),UTS and elongation of AA6010-0.6%Cu alloy were 370MPa,410MPa and 17.9%,respectively.The UTS increased to 420MPa when Zr and Ti addition,the UTS and elongation slightly increased when Ce and Er.Texture components of Al-Mg-Si-Cu alloy(T6 state)were Cube,CubeND(H),Brass,CubeND({001}<310>),{110}<011>and F and other textures.The increase of Cu content can promote the evolution of CubeND texture along {001} plane,and {110}<110>texture evolves into P texture.The recrystallization mechanism of the Cube band and the PSN nucleation were strengthened,however,shear band nucleation still the most important recrystallization mechanism.Ti and Zr can significantly inhibit the Cube and CubeND texture,and formed a stronger Copper and {110}<110>texture.Shear band nucleation was the most important recrystallization mechanism.Ce and Er can increased the strength of Cube texture,promoted the evolution of F texture,and significantly reduce {110} texture.Cube band nucleation were the important recrystallization mechanism,PSN and shear band nucleation were weakened.