| The Al-Mg-Si-Cu alloys not only own these properties, such as low density, excellent specific strength and plastic, but also own excellent electric and thermal conductivities. The strength can be enhanced by adding copper, but the intergranular corrosion sensitivity would be increaced. It’s a big obstacle to make the Al-Mg-Si-Cu alloy own these properties that high strength and good corrosion resistance. The influence of concent of copper and different solution methods on the microstructure, mechanical property and resistance to corrosion of Al-Mg-Si-Cu alloys were studied, by the means of microstructure observation, scanning of electron microscope, energy spectrum analysis, tensile testing and tracing the curve of electrochemical polarization. Besides, the mechanism of strengthening and corrosion resistance was dicussed. Some main research results are presented as the following:l)The segregation phenomenons of Al-Mg-Si-Cu alloys of different Cu contents can be observed, and the segregation phenomenon of high Cu content is more obvious than the low. The as-cast hardnesses of Al-Mg-Si-Cu alloys increace with the increasing Cu content; The grain boundary is likely to the thin line after taking homogenization treatment of570℃×10h, which stands for the process of homogenization is over. The segregation and internal stress can be eliminated after homogenization, and the plastic of Al-Mg-Si-Cu alloys will be improved.2) The second phase in the matrix will decrease with the time prolonging under different temperatures during the solution treatment, It will take fewer solution time under the higher temperature. After taking the treatment of54℃×4h, the process of recrystallization completed, and the second phase have mostly been dissolved without the phenomenon of grain growth.3) The hardness of the alloy is increased with the increasing of single stage of artificial aging time after taking solution teatment. After taking the single stage of artificial aging treatment of180℃X6h, The size deviation of the second phase is small, the distribution is well-distributed without the phenomenon of grain growth. The ultimate tensile strength and hardness of Al-Mg-Si-1.5Cu alloys are349.9MPa and105.84HB; After taking the double stage of artificial aging160℃×6h+200℃×2h, the sizes of second phase which precipitated during the pre-aging process will grow up, because these phases have the size advantage and easy to absorb the solute atoms surrounding, these grown up second phase make the hardness, tensile strength and the elongation rate all decline.4) The degree of supersaturation of alloy can be improved effectively by gradually increasing the solutionizing temperature, with the rusult that the precipitation of the second phase after aging will be promoted. The ultimate tensile strength of Al-Mg-Si-1.5Cu alloy can reach to395.9MPa after taking intensifying solution followed by single stage of artificial aging treatment, which increased nearly13%compared to the alloy after taking conventional solid solution; and the alloys after double stage of solution will make the matrix grain coarsing in different degree due to long time high temperature, it makes the tensile strength and hardness of alloys decrease after taking single stage of artificial aging treatment, respectively,280.3Mpa and78.8HB; and the effects of special solution treatments on Al-Mg-Si-Cu alloys containing high amount of Cu are more obvious than the alloys containing low amount of Cu.5)In the same corrosion conditions, the most severe intergranular corrosion is the Al-Mg-Si-1.5Cu alloy that after taking the conventional solid solution treatment followed by single stage of artificial aging, more91.9μm in depth compared to the alloy after taking high temperature pre-precipitation; The most severe intergranular corrosion is the Al-Mg-Si-1.5Cu alloy that after taking the intensifying solution treatment followed by double stage of artificial aging, more149.0μm in depth compared to the alloy after taking high temperature pre-precipitation; The subsequence (from deep to shallow) of intergranular corrosion of Al-Mg-Si-1.5Cu alloys that after taking different solution treatments followed by single stage of artificial aging treatment are Conventional solid solution, Intensifying solution, Double stage of solution,High temperature pre-precipitation; The subsequence (from deep to shallow) of intergranular corrosion of Al-Mg-Si-1.5Cu alloys that after taking different solution treatments followed by double stage of artificial aging treatment are Intensifying solution,Conventional solid solution, Double stage of solution,High temperature pre-precipitation.6)The corrosion potentials move towards the negative direction with the inceacing of Cu content after taking the conventional solid solution treatment followed by single stage of artificial aging, and the passivation region becomes narrower, and the corrosion current density is increased; For the alloys have the same content of Cu, the corrosion potential of the alloys that after taking single stage of artificial aging treatment is more negative than the alloys that after taking double stage of artificial aging treatment, thess results show that the corrosion resisting property of alloy that after taking double stage of artificial aging treatment is better than the alloy after taking single stage of artificial aging treatment.7)The subsequence (from positive to negative) of Ecorr of Al-Mg-Si-1.5Cu alloys that after taking different solution treatments followed by single stage of artificial aging treatment are High temperature pre-precipitation, Double stage of solution, Intensifying solution, Conventional solid solution; And the subsequence (from positive to negative) of Ecorr of Al-Mg-Si-1.5Cu alloys that after taking different solution treatments followed by double stage of artificial aging treatment are High temperature pre-precipitation, Double stage of solution, Conventional solid solution, Intensifying solution; The subsequences (from low to high) of Icon are the same as to the corresponding Ecorr. |
PDF Full Text Request