Study On Die Casting Technology Of High Strength And High Toughness Al-Cu Alloys

Nowadays, the usage of steels on vehicle parts has been taking place by die cast aluminum alloys world widely with high strength and hardness, long life span and good service performance. This project will be a key problem for us to solve in future.Considering the problem of low strength and toughness of die cast aluminum produced now, high strength and toughness Al-Cu die casting alloy and the die cast forming technology was studied in this paper.A new high strength and high toughness Al-Cu die casting alloy was developed through optimization of alloy composition, modification and heat treatment. The alloy composition was as follows(wt%): Cu: 5, Mn: 0.6—0.8, Ti: 0.15—0.25, V: 0.1—0.15, Zr: 0.05—0.1, Al: remains. The alloy has a best casting ability with the element content at the lower level and best mechanical property at the higher lever. The typical mechanical property after T6 heat treatment was: σ_b=350—375MPa, δ₅=3—5%.The study was mainly focused on the effect and mechanism as well of alloying elements and modification on casting ability of Al-Cu alloy. The results showed: Ti, B compound salts made the microstructure refined and increased the casting ability, Mn increased casting ability with a content below 0.6%;Both Ti and V gave a finer microstructure and better casting ability, however, a decline of casting ability could also be got if contents of Ti and V were above 0.2% and 0.15% respectively by segregation;With content below 0.1 %, Zr could refine the grains and enhance casting ability, but with a content over 0.1%, Zr decreased the casting ability when coarse phase would be produced.Low temperature aging heat treatment realized the heat treatment strengthen of HB die castings to some degree. After direct aging of 180°C, 8h, the mechanical property was: σ_b=300—310MPa, δ₅=8—10%.On the basis of optimization of die cast parameters, the effect of slow shot velocity on air entrapment during die cast was studied further according to slow shot theory. The resultsshowed that slow shot velocity had a great influence on density of HB alloy die castings. Die castings with highest density was produced when the critical slow shot velocity which was achieved by slow shot theory was adopted and therefore it can be concluded that the air entrapment can be decreased by critical slow shot velocity which subsequently made the T6 heat treatment of HB alloy die casting true.Best T6 heat treatment strengthen effect was abtained with 490°C, 3h solution and 180"C, 8h aging and the lower level of alloying element content gave an optimal mechanical property.