| Aluminum alloy has the characteristics of low melting point,low density,high specific strength,good electrical and thermal conductivity,and easy processing and forming.It is widely used in aerospace,biomedical,military,and other industries.The production of traditional aluminum alloys is mainly based on the casting process,and the phenomenon of coarse grains and element segregation are prone to occur during the forming process,which affects the mechanical properties of the aluminum alloy.Selective area laser melting(SLM)technology is a typical rapid prototyping technology that uses high-energy laser beams to melt metal powder to directly obtain high-performance,high-density complex metal parts.During the SLM forming process,the laser interacts violently with the alloy powder,the powder melts and solidifies instantly,and the melt cooling rate reaches 103-106 K/s,which can greatly increase the solid solubility of alloying elements and improve the mechanical properties of the alloy.Increasing the Mg content is an effective means to improve the mechanical properties of the Al-Si-Mg alloy formed by SLM,but too high Mg content will cause cold cracks in the sample and reduce the SLM formability of the alloy.The addition of Zr in Al-Si-Mg alloys can effectively refine the alloy grains and is expected to improve the formability of Al-Si-Mg alloys with high Mg content.Based on this,this study systematically studied the structure and mechanical properties of the Al-8.0Si-2.56Mg-0.41Zr alloy formed by SLM by adding Zr to the Al-Si-Mg alloy.details as follows:(1)Al-8.0Si-2.56Mg-0.41Zr alloy powder was prepared by aerosolization method.After analysis,about 90%of the powder has a particle size distribution between 20-60?m,with an average particle size of 38.29?m and powder sphericity.(2)The influence of laser power and scanning rate on forming quality.Studies have shown that at 190W,due to insufficient laser energy input and large internal stress,there are relatively porous and cold cracks in the formed sample,and the density of the sample is low,with a maximum of only 99.6%.Increase the laser power to 250 W and 350 W,and preheat the substrate to 200°C.There is no obvious defect inside the formed sample,and it is almost completely dense.The density of 350 W is higher than 250 W,indicating that the sample has good formability.(3)The influence of laser power and scan rate on the microhardness of the formed sample.Studies have shown that when the power is constant,the microhardness of the formed sample increases with the increase of the scanning rate;when the scanning rate is constant,the formed sample obtains a higher hardness value at 250 W.(4)Combining the influence of forming quality and microhardness,determine the best process parameters of SLM:laser power is 250 W,scanning rate is 1200 mm/s,at this time,the sample is almost completely formed densely and has a high hardness value.The metallographic structure of the Al-8.0Si-2.56Mg-0.41Zr alloy sample formed by SLM is dense,and the morphology of the molten pool is anisotropic.The tensile strength,yield strength,and elongation at break of the shaped samples were 464 MPa,426 MPa,and 1.4%,respectively.(5)After the formed samples are aged at 100-500?for 2h,the hardness of the formed samples increases first and then decreases rapidly with the increase of temperature.When the solution temperature is 165°C,the hardness of the sample reaches a peak value of 181.2 HV.Aging at 165?for different times,with the extension of the aging time,the hardness and strength of the formed samples are significantly increased.After aging for 12 h,the hardness and strength of the samples reach the peak.The maximum hardness is 190.6 HV,the maximum tensile strength is 522 MPa,and the maximum yield strength is 482 MPa.Its strength is significantly higher than that of the current Al-Si-Mg alloy formed by SLM,mainly due to the solid solution strengthening of Si,Mg and Zr elements and the Mg2Si second phase precipitated by aging. |
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