Microstructure And Properties Of Al-Cu-Mn Alloys By Laser Remelted

Al-Cu-Mn series aluminum alloys are widely used in aviation,aerospace,weapons,automobiles and other fields because of their high strength,heat resistance,good welding and processing properties,low price and low density.However,the existing alloys are difficult to be used normally for a long time under harsh conditions.Therefore,in order to meet the requirements of alloy properties in various fields,it is imperative to develop alloys with good room temperature properties and high temperature properties.Laser remelting treatment can significantly improve the undercooling and refine the surface grain,which has a very obvious effect on refining the surface grain size of as cast aluminum alloy,while heat treatment can further improve its mechanical properties and other service properties.In this paper,Al-Cu-Mn alloy is taken as the research object.In view of the difficulty of traditional cast Al-Cu-Mn alloy to meet the requirements of high strength and high wear resistance in aerospace,automobile and other fields,the surface of cast alloy is remelted by laser,and the laser remelted Al-Cu-Mn alloy material is prepared.The effect of laser remelting on the surface microstructure and properties of cast Al-Cu-Mn alloy is systematically studied,And the changes of microstructure and mechanical properties of matrix zone and remelting zone under different heat treatment processes.The phase composition and precipitate evolution of remelting zone under various heat treatment processes are analyzed in detail.The main research contents and results are as follows:(1)The effect of process parameters on the temperature field distribution of the alloy in the process of laser remelting was studied.The results show that in the process of laser remelting,the molten pool is symmetrically distributed in the X direction and elongated in the Y direction.At the front of the remelting zone,the medium temperature line of the alloy is densely distributed and its gradient is large,and at the rear of the remelting zone,the isotherm of the alloy is sparse and the gradient is small.When the laser power increases,the peak temperature of the molten pool,the width and depth of the molten pool also increase.When the scanning speed increases,the peak temperature of molten pool,the depth and width of molten pool decrease,but the change speed decreases.(2)The effect of laser remelting on the surface microstructure and mechanical properties of cast Al-Cu-Mn alloy was studied.The results show that the microstructure of remelting zone is mainly composed of equiaxed dendrites and fine columnar dendrites.After laser remelting?(Al)phase and?(Al₂Cu)phase was refined to a great extent.The T phase in the matrix is completely dissolved In the?(Al)matrix,Mn elements in the remelting zone are evenly distributed without segregation.The increase of hardness mainly consists of two strengthening mechanisms:fine grain strengthening and second phase strengthening.The hardness of heat affected zone is between remelting zone and matrix,and the hardness increases significantly with the increase of molten pool height.After remelting,the surface furrow is shallower and the wear debris is smaller than that of cast Al-Cu-Mn alloy.The wear mechanism of the alloy is mainly abrasive wear and adhesive wear.(3)The microstructure evolution and mechanical properties of laser remelting Al-Cu-Mn alloy matrix and remelting zone under different heat treatment processes were studied.Under the same aging process,the hardness of 530?solid solution for 4h is the highest,the matrix area is 80%higher than that without solid solution aging,and the remelting area is 59.1%higher than that without solid solution aging.The same solid solution process,with the increase of aging temperature,the shorter the time for the hardness to reach the peak,and the time for the remelting zone and the matrix to reach the peak is similar.The hardness of the matrix and the remelting zone reaches the highest after aging at 175?for 8h.After aging,the wear mechanism of alloy matrix and remelting zone is still abrasive wear and adhesive wear,and the friction coefficient of alloy decreases due to the increase of alloy strength.(4)The thermal stability of laser remelted Al-Cu-Mn alloy after direct aging was studied.The results show that the distribution of Mn elements in the matrix is gradually uniform with the extension of holding time when the laser remelted Al-Cu-Mn alloy is kept at 350?.When the temperature rises to 450?,the?(Al₂cu)phase shows obvious solid solution.After direct aging treatment,the hardness of the alloy matrix and remelting zone increases rapidly in the first few hours of heat preservation,and then fluctuates in a small range for a long time after the hardness decreases sharply.The main wear mechanisms are still abrasive wear and adhesive wear.