Study On Microstructure And Processability Of Composite Modified Al-30% Si Alloy

High-silicon aluminum alloy has many advantages such as wear resistance,heat resistance,small thermal expansion coefficient,good dimensional stability,excellent welding performance,etc.It is an important material for manufacturing engine cylinders,pistons,electronic packaging and other parts,and is widely used in aerospace and machinery,Automotive,electronics and other fields.However,the coarse and irregular polygonal plate primary crystal silicon and long needle eutectic silicon in the unmodified alloy structure severely cut the continuity of the matrix,making the alloy structure unevenly distributed,resulting in a significant decrease in the mechanical properties of the alloy and deterioration of the processing performance.Therefore,improving the alloy structure and improving the comprehensive performance of the alloy are the prerequisites for the high-silicon aluminum alloy to be widely used.Composite modification and heat treatment as an effective means of alloy strengthening have broad research fields and application prospects.In this paper,metallographic microscope,XRD diffractometer,tensile test,hardness measurement and other detection and analysis methods are used to study the effect of Sr,B and RE composite modification on the structure and mechanical properties of Al-30%Si alloy.Using precision plane grinder,dynamometer,scanning electron microscope,roughness measurement and other experimental methods and means,by changing the grinding parameters of the workpiece moving speed Vw and grinding depth ap,grinding force,grinding force ratio,grinding specific energy Surface roughness and surface morphology are evaluation indexes.The effect of composite modification and heat treatment on the grinding performance of Al-30%Si alloy was studied,and the grinding mechanism of the alloy was preliminary discussed.The research results are as follows:(1)Sr,B and RE composite modification significantly improves the alloy structure.The dendrite size and the distance between the secondary dendrites are reduced,and the densely distributed columnar dendrites are transformed into equiaxed crystals,which are uniformly distributed;the needle-shaped and strip-shaped eutectic silicon become shorter needle-shaped or short rod-shaped,or even It is granular and evenly distributed in the matrix;the primary crystal silicon changes from a sharp and thick plate to a five-star petal or is divided into fine particles,and the edges andcorners are dull.When the contents of B and Sr remain unchanged at 0.036% and 0.044%,respectively,and the RE content is 0.8%,the alloy structure is optimal.(2)The tensile strength of the composite modified alloy is significantly improved,compared with the unmodified alloy by 55%.When the RE content is 0.8%,the tensile strength of the alloy reaches the highest value of 90.1MPa.When the RE content is 0.8%,the alloy elongation is increased by 66% compared with the unmodified.When the RE addition amount is 0.8%,the alloy has the best plasticity.(3)The grinding force and the grinding force ratio both increase with the increase of ap and Vw,the grinding ratio can decrease with the increase of ap and Vw,and the influence of Vw on the grinding force is greater than ap;in the same Under the grinding parameters,the grinding force and grinding force ratio of the modified aluminum-silicon alloy are reduced,and the grinding ratio can be increased.When the RE addition amount is 0.8%,the overall grinding force and grinding force ratio are the smallest.The cutting energy is the largest.The effect of Vw on the surface roughness of the alloy is smaller than that of ap.The greater the ap,the greater the surface roughness.Under the same grinding parameters,the surface roughness of the composite metamorphic alloy is reduced by 44% compared with the uncombined metamorphism.When the RE content is 0.8%,the surface roughness is the lowest.It shows that after Al-30%Si alloy composite modification,it shows better grinding performance.(4)Under the same grinding parameters,the grinding force and surface roughness of the unheated alloy are the largest;when the heat treatment aging time is10 h,the grinding force and surface roughness are the smallest,the grinding surface processing quality is the best,and the alloy grinding The cutting performance is significantly improved.(5)The untreated workpiece has the largest grinding force ratio,followed by composite metamorphism treatment,heat treatment plus composite metamorphism treatment is the smallest;grinding specific energy is the largest heat treatment plus composite metamorphism treatment.(6)Grinding surface morphology is mainly formed by cracks,particle extraction,crushing of primary silicon particles,smearing of Al matrix,particle crushing and extrusion into Al matrix.