| The high-strength aluminum alloys are increasingly concerned by many scientific researchers due to their broad application prospects in the military and civil industries.ZL205A alloy is a typical high-strength cast aluminum alloy.The properties of the alloy can be effectively improved by appropriate heat-treatment process to obtain the good strength,hardness,ductility and corrosion resistance.In the thesis,the effect of different heat-treatment processes on the microstructure and properties of the alloy was studied by adjusting the process parameters.Assisted by OM,XRD,SEM,TEM,mechanical experiments including tensile,hardness testing and corrosion resistance experiments,the mechanical properties and corrosion resistance of the alloy were analyzed.The mechanism of microstructure evolution which regulates the properties of the alloy,was explored.The superior heat-treatment process was explored in order to improve the comprehensive properties of ZL205A alloy.The results show that 538?×15h is the optimal single-stage solution treatment process.Furthermore,the double-stage solution treatment process is explored:530?×2h+540?×13h.Ultimate tensile strength,yield strength and elongation of the alloy are 338.9 MPa,161.30 MPa and 22.3%,respectively.The coarse eutectic network structure of as-cast ZL205A alloy was dissolved by solid solution treatment to obtain supersaturated solid solution,which provided good microstructure conditions for aging treatment.The mechanical properties of ZL205A alloy are greatly improved by double-stage solution and aging treatment.Meanwhile,the alloy has obvious performance advantages under double-stage solid solution+155?×8h/165?×6h/175?×6h/185?×5h aging process,respectively.The results show that the?b of the alloy reaches the peak value of 501.12 MPa at 175? for 6h.The?0.2 and?of the alloy are the largest at 155? for 8h,419.41 MPa and 7.88%,respectively,while the hardness of the alloy is 167.57 HV at 185? for 5h,and the comprehensive mechanical properties of the alloy are better at 165? for 6h than other aging treatment alloys.The?b,?0.2,HV and?of the alloy are 493.84 MPa,394.81MPa,164.20 HV and 6.90%,respectively.After aging 175?×6h,the mechanical properties of ZL205A alloy at 300? were investigated.The results show that the?b,?0.2,and?of ZL205A alloy are 285.41 MPa,245.49 MPa and 13.6%,respectively.The high temperature mechanical properties of the alloy were improved.?'is the strengthening precipitate of the alloy.With the increase of aging temperature,the size of?'increases,while the volume fraction and aspect ratio decrease.At the same time,?'phase becomes more stable,which can effectively inhibit the dislocations movement and improve the mechanical properties of the alloy.The corrosion resistance of ZL205A alloy was studied by immersion tests and electrochemical experiments.The results show that the corrosion resistance of ZL205A alloy can be effectively improved by double-stage solution+aging treatment.The corrosion resistance of alloys in different states decreases in turn:185?×5h>175?×6h>165?×6h>155?×8h>as-cast alloy.The?'phase of 185?×5h aging alloy is large and scatters in the matrix,which is beneficial to block the corrosion channel and enhance the corrosion resistance of the alloy.Observing the Tafel curve and corrosion morphology,it was found that pitting corrosion occurred in different state alloys during galvanization,and galvanic corrosion caused by grain boundary corrosion microbatteries was the main reason for pitting corrosion.In conclusion,the microstructure of ZL205A alloy is optimized by double-stage solution+aging treatment,and the superior alloy under different heat treatment systems is obtained,which effectively improves the comprehensive properties of the alloy and provides the theoretical basis for the practical application of ZL205A alloy. |
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