Effect Of Rare Earth And Hot Extrusion On Microstructure And Properties Of Al-Si-Cu-Mg Alloy

Eutectic-near Al-Si-Cu-Mg alloy is good at casting and has high strength and other characteristics, so it is extensive used in industy. The effect of rare earth has been studied in this paper. The effect of rare earth elements on the strength nature has been studied. The relationship between hot extrusion and mechanical properties of alloy has been investigated by observing the breaking mechanics of the second-phase.The effect of rare earth Ce and RE addition to Al-Si-Cu-Mg on the mechanical properties of alloys shows different ways. The effect of mixed rare earth RE to mechanical properties is much more apparent than that of single Ce. With the increase of Ce,RE in Al-Si-Cu-Mg alloy , the existent form of Ce,RE has changed. Rare earth elements may form intermetallic compounds with various elements in the alloy, and when the content of rare earth excesses , there will be some big blocks which are rich of Ce and RE.Both addition of rare earth Ce and RE into the Al-Si-Cu-Mg alloy aging at 175℃let to a double aging peaks. The addition of Ce and RE improves the hardness and slows the velocity of hardness-aging of Al-Si-Cu-Mg alloy and postpones the occure of hardness peaks of aging treatment and soften of over- aging.By analyzing the SEM photo of Al-Si-Cu-Mg alloys , it is founded that the eutectic-Si can be divided into 3 stages: during the early stage of solution treatment, the dissolution of Si-phase improves the tensile strength of alloy; during the intermediate stage graduation the tensile strength of alloy has become the peak value; during the coarsening process Si-phase tensile of the alloy decline. Both the heat treatment processing and the aging process improve the strength of the alloy.The strain during the process of hot extrusion has also been investigated. The result of the simulation shows that: the strain has mainly happened in the formed and slowly flowing areas; the top areas of sizing slows lower normal strain; there is no strain in the unformed areas. The result of the experiment shows that strain and extrusion ratio are in direct proportion; the larger the extrusion ratio, the higher the breaking stress; the second-phase in the unformed areas has not broken fundamentally; the second-phase in the formed areas has one time broken fundamentally and became stick shellac and small quantity granular; the effectiveness of breaking of second phase is the best and the long acicular and lath shaped phase can break a lot of time and the cube-formed edge angle has been passivatted in this area, the sizing area is the last formed area and has little breaking.Hot extrusion makes the mechanical properties of alloy wide-range improved and the ultimate tensile tension reach 308.6MPa, 30% higher than that in the condition of metal-casting; elongation percentage reaches 30.6%, higher 950% than that of metal-casting; after T6 heating processing , the tensile strength reaches 400 MPa and elongation percentage also reaches 18.8%o With the increase of extruding ratio, tensile strength and elongation percentage has also been improved.