| The concept of lightweight stimulates the development of aluminum alloys which are widely used in various fields such as aerospace and automobile manufacturing,and this causes a great deal of aluminum alloy scraps being produced.A356 aluminum alloy is widely used in automobile wheel and other component manufacturing because of its good formability,medium strength,and good corrosion resistance.Based on the environmental protection concept of green manufacturing,and combined with the traditional theoretical basis of large plastic deformation,this research used hot extrusion-forging and high energy ball milling combined with hot extrusion to prepare Al-Si-Mg/Fe aluminum alloy bulk materials for solid state regeneration of A356 aluminum alloy machining chips.The investigation focus on the relationship between the structure and tensile properties of the bulk material,and try to provide an effective reference for improving the recycling value of aluminum alloy scraps.The effect of different deformation variables on the microstructure of direct thermomechanical consolidation(hot extrusion-forging)Al-7Si-0.3Mg aluminum alloy was studied.It was found that a large amount of plastic deformation caused dynamic recrystallization of Al(Si,Mg)grains and breaking of Si(and Al3FeSi)particles,and more uniform distribution of them in the microstructure of the material.At the same time,the breaking of the ?-Al2O3 thin film at the interparticle boundaries made the material achieved a good interface metallurgical bonding effect.After T6 heat treatment,the equiaxed grains of Al(Si,Mg)grains in the hot-pressed and extrusion-forged samples were transformed into elongated deformed grains,and coarsened to varying degrees,the reason of which was the presence of fine ?-Al2O3 particles restricted the mobility of interparticle boundaries.It was found that the extrusion-forged samples showed good performance before and after T6 heat treatment.Especially after T6 heat treatment the sample exhibited a yield strength(YS)of 228 MPa,an ultimate tensile strength(UTS)of 275 MPa,and an elongation to fracture of 8.4%,which all indicate better mechanical properties than the traditional cast A356 aluminum alloy.The HP-T6 sample had similar YS,but fractured quickly after yielding,with very little strain.This was because during the tensile test process,the microvoids formed by the fracture of the Si particles were rapidly expanded until they broken through the interparticle boundaries with weak bonding force.Therefore,reducing the size and content of ?-Al2O3 particles at the interparticle boundaries can improve the interface bonding effect of the material and enhance the ductility.The extrusion-forged samples show good ductility before and after T6 heat treatment,which illustrates that the additional plastic deformation makes interface crack exists in the interparticle boundaries finer,and exposes fresh atomic surface to establish more effecti ve interface bonding.Nanostructured Al-7.2Si-2Fe(wt.%)and Al-7Si-5Fe alloy powders were fabricated with A356 aluminum alloy machining chips and gray cast iron machining chips by high energy ball milling.The research used room temperature cold pressing(CP)-hot extrusion(HE)and spark plasma sintering(SPS)combine with hot extrusion(HE)to fabricate bulk ultrafine structured Al-7.2Si-2Fe and Al-7Si-5Fe alloy samples,and investigated their microstructures and mechanical properties.The Al-7.2Si-2Fe and Al-7Si-5Fe alloys fabricated by CP+HE had the average Al(Si,Mg)grain sizes of 1.8 and 1.3 ?m,respectively.The average Al(Si,Mg)grain sizes of Al-7.2Si-2Fe and Al-7Si-5Fe alloys prepared by SPS+HE were 2.6 and 1.5?m respectively.The SPS did not cause abnormal coarsening of the grains.The increase of Fe content increases the chance of dynamic recrystallization nucleation during hot extrusion,which results in the average grain size of Al-7Si-5Fe aluminum alloy become smaller.The YS,UTS and elongation to fracture of Al-7.2Si-2Fe and Al-7Si-5Fe aluminum alloys prepared by CP+HE were YS:375.5 MPa and 477.9 MPa;UTS:372.7 MPa and 489.0 MPa;and elongation to fracture:0.2%,0.1%,respectively.The SPS+HE samples of the Al-7.2Si-2Fe and Al-7Si-5Fe alloys had YS of 397.4 and 489.4 MPa,UTS of 416.2 MPa and 507.8 MPa;elongation to fracture of 0.9%and 0.3%,respectively.The strength of Al-7.2Si-2Fe and Al-7Si-5Fe samples is significantly higher than that of the ultrafine structured Al-7Si-0.3Mg aluminum alloy rods prepared by similar methods,but the tensile ductility of the former is poor.The fracture is typically brittle fracture,mainly consist of intercrystalline fracture,and some have quasi-cleavage fracture characteristics.The reason for the poor ductility is that the microcracks that originate from the broken Si particles quickly expand in the matrix and the limited plastic deformation of nanostructure,which causes the material to fail after a small plastic deformation. |
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