Abstract: A horizontal-type twin roll casting method has been popular for producing aluminum alloy strips, however, it is characterized by a relatively low productivity (1~6 m/min). In contrast, a vertical-type high-speed twin-roll casting method possesses an extremely high productivity (60~120 m/min (1~2 m/s)) and an excellent heat extraction ability. The rapid cooling effect provided significant microstructure refinement and mechanical properties improvement in various kinds of cast aluminum alloy products. Not only “product to product recycling” but also “up-grade recycling” can be achieved by making good use of these merits. Two examples of application showing the potential of vertical-type high-speed twin roll casting method are presented. (1) Several kinds of Al-Si base alloy were cast into the strips. Not only strength and toughness but also formability was increased in the twin roll cast products. In particular, great improvement in deformability shows the potential of the twin-roll cast aluminum alloy products as substitutes for some wrought aluminum alloy products. (2) The vertical-type tandem twin-roll caster was able to fabricate a clad strip by single step. The A4045/A3003/A4045 aluminum alloy clad sheets produced by the twin-roll casting showed better mechanical properties than the conventional hot-roll bonded clad sheets.
Abstract: Parts of thermal physical properties of Al-Si8-Cu2-Mg alloy were studied. The curves were plotted showing the relationship between density, specific heat capacity, coefficient of thermal expansion and the variation of temperature for the first time with this alloy. The results show that the density was decreased when the temperature was raised, but the specific heat capacity and the coefficient of thermal expansion were first increased and then decreased. The solidus-liquidus temperatures, latent heat of fusion were studied, and the results show that the melting temperature range of this alloy was 507-596°C.
Abstract: In order to reduce the adhesion tendency of aluminum melt on the die casting mold and extend the service life of the die, multi-arc ion plating technique was used to deposit Ti/TiN/CrN multi-layer coating on the surface of 8418 hot-working mold steel. Corrosion resistance of the steel and the Ti/TiN/CrN coating against Al alloy melt was studied. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to study the microstructure, phase constituent and phase composition of the materials. Uniform Ti/TiN/CrN coatings with good bonding interfaces and a total thickness of about 2 μm were obtained. Results showed that Ti/TiN/CrN coating can improve the corrosion resistance of the 8418 hot-working die steel significantly against the aluminum alloy melt.
Abstract: Supersaturation behavior of Al solid solutions and its effect on tensile property in Al-7Si-0.4Mg and Al-7Si-0.8Mg alloys during solution heat treatment were investigated in this study. As a result of Mg solubility measurement for Al solid solitions after solution heat treatment for 6 hrs by electron probe micro analyzer (EPMA)-wavelength-dispersive X-ray spectroscopy (WDS), Al-7Si-0.8Mg alloy had the higher Mg solubility, about 0.55 mass%, corresponding to that of Al-Si-Mg ternary phase diagram. From the tensile test, Al-7Si-0.8Mg alloy showed the improved strength and similar elongation to that of Al-7Si-0.4Mg alloy.
Abstract: Present work was carried out to investigate the measurement accuracy of the sump depth for 7050 billet in direct chill (DC) casting process. Three measuring methods were applied: (i) Al-30wt.% Cu melt was poured into the mold at the steady state of the casting attempting to record the profile of billet sump; (ii) two steel rods were vertically dipped into the centreline and the edge of the billet attempting to measure the distances between the solidus and the free liquid surface in the hot-top; (iii) several ordered thermocouples were pre-arranged onto the starting block and they were solidified into the billet as it was cast, and a series of temperature-time curves was recorded after casting. For the purposes of comparison and evaluation, a numerical model based on the same experiment parameters was also built and the simulation results were compared with measured results by above methods. It indicates that the sump depth measured by thermocouples has the best consistency with numerical results. The most accurate method is temperature recoding by thermocouples. The Al-Cu melt pouring method is more accurate than the rods dipping method, and the sump depths measured by later two methods were the positions about the solid fraction (fs) depths of 0.8 to 0.9.
Abstract: A low frequency electromagnetic field was introduced into the direct chill (DC) casting process and the ingots of Al-Cu alloy were prepared to study the macrosegregation behaviour of the ingots under the influence of the electromagnetic field. The experimental results showed that there is an obvious positive segregation near to the surface and a negative segregation in the centre area of the ingot. Cu shows the highest segregation tendency among the main elements of Cu, Mg and Mn. Grain refiner element Ti shows a segregation trend opposite to that of Cu. With the application of electromagnetic field, the negative centreline segregation in the centre area of the ingot was evidently reduced although it didn’t show significant effect on the segregation near to the ingot surface. A significant grain refinement was also achieved with the application of electromagnetic field. The mechanism of the reduction of macrosegregation with electromagnetic field was also analyzed in the present work.
Abstract: To study the micromechanics of semisolid deformation, a modified experimental set-up is employed in Gleeble 3800 thermomechamical testing unit to achieve a uniform temperature distribution in partially remelted aluminum samples. The temperature variation was markedly reduced to one degree for a length of 4-5 mm in the middle of tensile samples. High temperature semisolid tensile tests of Al-Cu 206 cast alloys were performed at different temperatures near solidus with a strain rate of 10-3 s-1, corresponding to the solid fractions (fs) between 1 and 0.95. The stress-displacement curves with different fs were measured and analyzed. The microstructure and fracture surface of samples were examined by optical and scanning electron microscopes. The relation between the microstructural characteristics, tensile properties and fracture behavior of semisolid 206 samples at high fs were explored. Mush deformation mechanisms were discussed in term of defect nucleation and propagation at the late stage of solidification.
Abstract: Sb is an effective additive to modify eutectic Si of Al-Si alloys and the modification mechanism has not yet been studied very clearly. In this paper, computer aided cooling curve thermal analysis and microstructure assessment were carried out to investigate the modification effects of Sb on Al7SiMg alloy. The results show that the Sb addition amount of 0.1~0.25% has improvement effect on eutectic Si morphology, which can be further confirmed from the thermal analysis results. The addition of Sb decreases the eutectic growth temperature by 5 °C to 7.8 °C, indicating an undercooling effect resulted from Sb modification. Compared to that of short rods, a better eutectic Si morphology of nearly granular particles can be obtained in a faster cooling rate. The length of silicon has been gradually shortened as holding time increased to 2.5 h from 0.5 h, which means a long period modification effect of Sb in Al-Si alloys. Owing to undercooling resulted from Sb addition in Al-Si alloys, the refinement structure of eutectic silicon can be achieved.
Abstract: The grain refinement in a high specific strength Al-Zn-Mg-Cu casting ingot was studied by add different amount of Al-Ti-C and Al-Ti-B master alloys during casting. The optical microscopy observation shows that the grain size of ingot is greatly reduced when adding Al-Ti-B as low as 0.01 wt%. Both the average size and the size difference among samples from various locations of ingots are smaller when the alloy casted with Al-Ti-B, which indicates that Al-Ti-B is effecient for the grain refinement in the Al-Zn-Mg-Cu casting ingot.
Abstract: Effects of Si addition on the microstructure, fluidity and tensile property of Al-5/7mass%Mg alloys with Mg+Al2Ca master alloy as Mg raw material were investigated in this study. With 7 mass%Si addition, the fluidity was remarkably improved in both Al-5Mg and Al-7Mg alloys. With increasing the Si content, the amount of the eutectic phases was increased in the microstructures. As a result of the tensile test, there was a drastic reduction in elongation with increasing Si content. Al-5Mg-7Si alloy showed a significant improvement of strength after solution heat treatment and artificial aging.