Materials Science Forum Vol. 877

Abstract: The AA4045/AA3003 cladding billet, which has a low clad ratio of 7.5% in size of φ160mm/φ148mm, was prepared successfully by the modified direct chill casting process. Microstructures, elements distribution and mechanical properties of the bonding interface were examined. The results show that metallurgical bonding interface can be obtained with the optimal parameters. The metallurgical bonding interface is free of any discontinuities due to the elements diffusion across the interface. The hardness of the interfacial region is higher than that of the AA3003 but lower than that of AA4045, suggesting that the interface bonding strength is higher than the strength of AA3003. The shearing strength is 82.3 MPa, indicating excellent metallurgical bonding.

Abstract: AA4045/AA3003 cladding billets with different clad ratios were fabricated by direct chill casting process. The macrostructures, microstructures, compositions distribution and the mechanical properties near the bonding interface were investigated in detail. The results show that the cladding billet with few defects could be obtained by semi-continuous casting process. The metallurgical bonding was formed due to the diffusions of elements. The decreasing of clad ratio changed the microstructure at the interface and reduced the thickness of diffusion layer. The hardness around the interface is higher than that of AA3003 side but lower than that of the other side, indicating that the interface yield strength is also higher than that of AA3003. After extrusion process, the characteristics of the interface remain that of as-cast cladding billet.

Abstract: The aim of this work is to investigate the effect of different casting speed in DC casting process and solution heat treatment of in situ Al-13.9%Mg₂Si composite. The increasing of DC casting speed not only makes primary Mg₂Si distribute more uniform and restricts segregation of primary Mg₂Si particles, but also it reduces primary Mg₂Si particle size. The DC casting speed significantly alter the eutectic Mg₂Si phase from fibrous to fine dot-like and eutectic phase refines effectively. The results obtained from mechanical testing demonstrated that the increasing of DC casting speed intensifies both hardness and tensile strength values. Then, the billet were subjected to solutionizing at 500^oC for holding time of 4h followed by quenching. The results indicate that the morphology of both primary and eutectic Mg₂Si changes after heat treatment. Solutionizing leads to the dissolution of the Mg₂Si particles and changes morphology from sharp edges to round shape. After solution heat treatment, tensile strength and elongation increase to 238.8MPa and 13.5%.

Abstract: Effect of cooling rate on modification and refinement of 4032 aluminum alloy has been investigated at cooling rates of 0.7~4.5 K/s. Sr is used to modify eutectic silicon and B is used to refine primary α-Al grains. Modification level of eutectic silicon and refining results of primary α-Al are characterized quantitatively by L_p based on the perimeter of eutectic silicon particles and the maximum grain length D, respectively. As the cooling rate decreases, the needle-like eutectic silicon particles increases and the modification level reduces with a constant Sr content. Influenced by alloying elements such as Mg, Cu and Ni, the modification level is very low at the lowest cooling rate of 0.7 K/s, but properly increasing Sr content in the melt can improve the modification. At the cooling rates of 0.7~4.5 K/s, the element B can transform coarse columnar dendritic α-Al grains to equiaxed ones, and controlling the ratio of Sr and B is a valid technique to avoid mutual poisoning. On the conditions of present experiments, the Sr content of 350 ppm and Sr:B ratio of about 1.1 are rational to modify eutectic silicon and refine primary α-Al grains simultaneously.

Abstract: The effect of phosphorus on primary silicon, phosphorus and mischmetal (Ce-50La) modification on primary and eutectic silicon and cooling rate on microstructure of Al-25%Si are investigated. The results show that, with the addition of phosphorus, the size of primary silicon decreases from 93.6μm to 24.75μm. The morphology of primary silicon changes from irregular to polygonal. When Al-25%Si is modified by phosphorus and mischmetal, primary and eutectic silicon all change effectively. Addition of mischmetal on the basis of phosphorus modification have no influence to primary silicon, but it can make morphology of eutectic silicon change from lamellar to short rod-like when the content of mischmetal reaches 0.5%. The cooling rate curves show the change of temperature in different height of wedge-shaped mould. When cooling rate increases, microstructure of Al-25%Si refines, the size of primary silicon decrease to 22.7μm. The results obtained from mechanical testing demonstrate that the addition of mischmetal and increasing of cooling rate increase hardness value of Al-25%Si alloy.

Abstract: Iron contamination from scrapped materials is always a problem in producing high quality secondary aluminium alloys. Consequently, the iron removal during recycling of aluminium alloys is essential and important in industrial practice. This work aims to study the effect of extra Mn addition on the effectiveness and efficiency of iron removal during recycling. The thermodynamics assessment was carried out for Al-Si-Cu alloys to find out the variation of balanced iron and manganese in the liquid melt and in the sediment solid Fe-rich intermetallics with different levels of extra Mn addition. The effect of alloy composition and processing temperatures was investigated. The findings help to understand the capability and fundamentals of iron removal in aluminium alloys.

Abstract: The present work deals with the relationship between microstructure and mechanical properties of A356 aluminum alloy which was produced via thixocasting process under different casting conditions. Feedstock billets were heated to a target temperature to obtain a semi-solid slurry with the required solid fraction. Some billets were heated to a fully-melted condition. In order to obtain fine and spheroidized Al grains, some billets for the partially melting were compressed axially by 33% at a room temperature before heating. The completely-melted and partially-melted slurries were die-cast by using a die-cast machine, and hour glass-shaped rod-type tensile specimens and small-size plate-type tensile specimens were obtained. Small cubic specimens were also collected from the die-cast products for microstructural evaluation. They were polished, and etched by Weck’s reagent. The partially-melted specimen which was compressed before heating shows the spherical Al grains. But the grain of the strain-free partially-melted specimen exhibited complicated morphology. The fully-melted specimen shows the fine and dendrite structure.

Abstract: A vertical type twin roll caster with two side dams was used to cast aluminium alloy strip with a thickness of about 5mm at speed higher than 10m/min. The characteristics of the twin roll caster with two side dams are as follows: The diameter of the copper roll is 500mm, the width of the copper roll is 110mm and the thickness of the copper roll sleeve is 25mm.The maximum casting speed is up to 60m/min. Using the vertical type twin roll caster, a 4.5mm thickness of 6111 strip could be cast at a speed of 30m/min. The microstructure of the as-cast strip was equiaxed and spherical, not columnar. The mechanical properties of the strip casted from the vertical type twin roll caster were almost as same as that of the strip made from the conventional cast ingot.

Abstract: For decades, twin-roll casting has been applied for manufacturing aluminum alloy sheets. This conventional process contributes to make thin aluminum sheets from the molten metal directly. Recently, vertical-type high-speed twin-roll casting (HSTRC) has been developed with much higher casting speed rather than the horizontal-type. Some modifications such as feeding nozzle and water-cooling system of copper rolls contribute to increase cooling rates. This characteristic leads to many metallurgical advantages like grain refinement, super-saturation of alloying elements and fine distribution of secondary particles. The objective of this study is to investigate the constituent particles in HSTRC aluminum alloy. The commercial Al-Mn alloy strip was successfully fabricated by HSTRC. Clearly different microstructure was found in thickness direction. Many constituent particles observed along the grain boundaries/cell boundaries as well as inside of Al matrix on the surface area, while eutectic structure around globular grain boundaries was observed in mid-central area. The morphology as well as chemical compositions of the constituent particles were investigated.