| Aluminum alloys as traditional metal materials with lower density, higher specific strength, heat machining capability,are widely used in aerospace, automobile. With the rapid development of modern industry, the need of structures existed stengthen and toughening and light-weight together is urgent. applications of Aluminum alloys will become more and more wide. as a result, people demand for as-cast Al alloy with more higher mechanical properties. So the high strength and toughness aluminum alloys has its development chance to research and applications. in system of aluminum alloys, Al-Cu alloy turn into hot focus of high tensile strength and ductility aluminum alloys,because of its well mechanical properties. However, Al-Cu alloy as a high tensile strength and ductility aluminum alloy, has poor corrosion resistance.its applications have potential hazard to bring tremendous economy loss and catastrophic accident. So the applications are limited for intergranular corrosion mainly. when strength and ductility of Al-Cu alloy is researched, its corrosion resistance is investigated at the same time,which have important signification of theory and practice.Al-Cu alloy is researched as a target for its properties , the present study has utilized a heat treatment optimization, based on the orthogonal design.the Aluminum alloys with higher tensile strength and ductility were made by feasible casting methods.the effects on the casts properties and microstructure of the rare earth oxides and heat treatment are investigated. And strength-ductility and corrosive mechanism of Al-Cu alloy is researched preliminary. strength-ductility mechanism will be understanded further and system of high tensile strength and ductility aluminum alloys will be enriched for my research, which has important signification of theory and practice to make high tensile strength and ductility aluminum alloys.The results showed: the Al-Cu alloy with high tensile strength about 520MPa and enhanced ductility about 13.5%,was made after T6 heat treatment(510℃*15h+165℃*10h)by orthogonal experiment, well mechanical properties of the alloy are not reported in home and abroad provisionally. Its application will be wide and nice. There has developed in recent years a renewed interest in the influence of grain size on the mechanical properties of materials. It is anticipated that these properties may be enhanced by a reduction in grain size. We believed that rare earth oxide had positive effect to reduce grain size and fine microstructures, grain sizes of unmodified alloy with rare earth oxide was 70-100μm after T6 heat treatment ,but grain sizes of modified alloy was 30-50μm at the same heat treatment. In this paper, technics of heat treatment were researched to acquire following rules: solid solution strengthening was a important approach to strength-ductility of the alloy by the range analysis. Way to obtain better tensile strength: 510℃*15h+165℃*10h; Way to obtain better elongation: 520℃*9h+ 165℃*5h;best scheme of mechanical properties by the range analysis accord with fact fitly. Effects of solid solution temperature, solid solution time, aging temperature and aging time on the microstructures of Al-Cu alloys was studied detailedly.At the same solid solution time,effect of solid solution was improved with increase of solid solution temperature, however, when solid solution temperature was over 530℃,casting samples appeared thermal overload phenomenon. At the same solid solution temperature, effect of solid solution was improved with increase of solid solution time, grain begun to grow up at the same time.At the same aging time, second-phase particles was more with increase of aging temperature, second-phase particles grow up at the same time.At the same aging temperature, grains begun to grow up with increase of aging time, when aging time got to 20h, aging microstructure was bad.Making of higher tensile strength and ductility aluminum alloys interrelated with appropriate technics of heat treatment closely. Research of technics of heat treatment in this paper had important practical meaning and make base firmly to uncover strength-ductility mechanism. corrosion resistance of the Al-Cu alloy was researched by corrosion weight lose, the structure after corrosion, polarization curves, corrosion potential.we saw that corrosion resistance of modification alloy was improved. When the content of rare earth oxide was to1.5wt.%, the corrosion resistance of the alloy was the best, while when the content of rare earth oxide was 2.0wt.%, the corrosion resistance of the alloy is falling. Addition of rare earth oxide may improve the corrosion resistance as a new way and direction. strength-ductility mechanism of Al-Cu alloy is researched preliminarily in this paper. I thinked that ways of strength-ductility could be realized by solid solution strengthening ,grain refinement strengthening and the second-phase strengthening mainly.but the best important strengthening for Al-Cu alloys was the second-phase precipitation strengthening, effect of strength was better because of the large amount of second-phase particles and their small space. Microstructures of the alloy became fine for the addition of rare-earth oxide obviously, which restrain second-phase particles to close grain boundaries, second-phase particles distribute in inside of the grains and grain boundaries evenly.when locomotive dislocations were blocked off by small second-phase particles, dislocations rounded second-phase particles for undistortion,which enhanced density of dislocations to improve strengthening effect of heat treatment. Al-Cu alloys had poor corrosion resistance.the intergranular corrosion of the Al-Cu alloy was caused by second-phase precipitation in grain boundaries and precipitate free zone in near area. As different corrosion potentials among precipitate phase, precipitate free zone,grain self; when corrosion medium existed, numberless electrochemistry tiny-batteries came into being.which resulted in chunnel of anode dissolve over grain boundaries,this was intergranular corrosion. for the addition of rare-earth oxide obviously, which restrain second-phase particles to close grain boundaries, second-phase particles distribute in inside of the grains and grain boundaries evenly,which the susceptibility of corrosion decreased greatly. Comparing with unmodified alloys,Al alloys modified with rare-earth oxide have well corrosion resistance under the same corrosive condition(dipped in 3.5wt% NaCl solution ).To sum up, although casting aluminum alloys have wide and beautiful future, research and applications of aluminum alloys are a challenge rigorously. Firstly, With the rapid development of modern industry, demands for security and integration properties of castings are enhanced continually. How to keep traditional casting aluminum alloys develop in new century. How to explore new aluminum alloys to meet various needs. These tasks are faced to make traditional casting aluminum alloys brilliant. I think that development of high tensile strength and ductility aluminum alloys will centralize following aspects:(1) using high pure material of industry,and reducing volume fraction of Fe , Si metallic compound, mechanical properties of casting are improved by reducing blowhole, dispersed shrinkage and stress centralization.(2) using appropriate technics of heat treatment, aging treatment especially, control microstructures of aluminum alloys in order to obtain well mechanical properties .High tensile strength-ductility and corrosion resistance are unified.(3) strength-ductility and corrosive mechanism of Al-Cu alloy is researched further. In conclusion,during understanding material,people bring forward new needs and technics. We may see that more scientific heat treatment and higher mechanical properties of aluminum alloys will appear continually.
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