Industrialization of Aluminum Alloy Uniform Solidification Controlled Rheological Die Casting

An efficient and low-cost aluminum alloy uniform solidification control technology, namely, air-cooled stirring rod (ACSR) process, has been developed for preparing large volume semisolid slurry. The semisolid slurry preparation process is connected with the die-casting machine to form multiple integrated intelligent rheological die-casting production lines for the efficient preparation of rheological die-casting of large-scale thin-walled aluminum alloys. At present, the ACSR process can produce 40 kg of large-volume semisolid slurry with a solid phase ratio of 25% to 35% within 30 s. This rheological die-casting process has been industrialized for the preparation of high-quality aluminum alloy large-scale thin-walled parts, such as new energy vehicles and 5G communications. Typical products produced by this process include heat dissipation housings for 5G communications, filter housings, antenna chassis and three-electric structural shell, end cover, and ABS system valve body for new energy vehicles. Compared with traditional die castings, aluminum alloy castings prepared by the new process not only have fine and spherical microstructures, good surface quality, and fewer internal pores but also enjoys more excellent mechanical properties and thermal conductivity.

Semisolid Casting and Die Casting of Al-4.8%Mg-2%Si Alloy

An aluminum alloy, Al–4.8%Mg–2%Si, was cast by die casting and thixocasting, and the properties of the cast specimens were investigated. When the poured molten metal temperature was lower than 640 °C during die casting, it was lower than the liquidus temperature, and the metal became a semisolid slurry in the sleeve of the die casting machine; this fulfills the conditions for rheocasting. A tension test was conducted to investigate the effects of semisolid casting on the mechanical properties of Al–4.8%Mg–2%Si. The ultimate tensile strength and elongation of the ingots cast by die casting and rheocasting were affected by the size of ingot. When the ingot had a circular base of 4.5 mm diameter, the ultimate tensile strength and elongation were excellent; however, when the cross section of the ingot was a square with a side length of 20 mm, the tensile strength and elongation were inferior. The thixocasting was conducted using square ingots with a side length of 20 mm, and the tensile strength and elongation were poor in this case as well. The results of this study demonstrate that semisolid casting cannot improve the mechanical properties of Al–4.8%Mg–2%Si ingots with a high thickness. Semisolid casting cannot produce fine-grained Mg2Si, and the mechanical properties of the material could not be improved by this casting method.

Effect of Pouring Temperature on Mechanical Properties of Semisolid Cast A319 Aluminum Alloy

Semisolid metal (SSM) casting or thixoforming is a technique used to produce near net-shaped products. The process is used with non-ferrous metals, such as aluminium, copper and magnesium. Furthermore, it has advantage over conventional casting due to suppression of dendrite growth. In the present work, the semisolid casting of A319 aluminium alloy has been carried out by using an inclined plate with different melt pouring temperatures (620, 625, 630 and 635 °C). A319 alloy melt undergoes partial solidification when it flows down on an inclined plate. It results in continuous formation of columnar dendrites on plate wall. Due to forced convection, these dendrites are sheared off into equiaxed or fragmented grains and then washed away continuously to produce semisolid slurry at plate exit. The prepared castings were checked for their mechanical properties like tensile, hardness and impact strength. The results obtained were compared with that of alloy prepared from conventional sand casting. It was found that there is an enhancement in mechanical properties due to shearing off columnar dendrites.

Thixoforming of Semisolid Slurry with High Fraction Solid Fabricated by Partial Melting of Commerical Wrought Aluminum Alloys

Semisolid slurries of four wrought alloys were fabricated via partial melting of commerical wrought aluminum alloy. Thixoforming experiments of four typical parts were performed. The results showed that a large amount of equiaxed grains before soaking in semisolid state were created due to recrystallization occurred in the continuous heating from room temperature to a given temperature above recrystallization temperature. It provides a desirable microstructure to form spheroidal grains during the next soaking process in semisolid state. The microstructure of the 2A12,7A04 and 7075 semisolid slurry consisted of fine and spheroidal grains. The elongation of the thixoformed parts were higher those of the hot-rolled plate. The UTS of the thixoformed parts were close or ever higher than those of the hot-rolled plate. Although the grain size and roundness of the 5A06 semisolid slurry are not very desirable, the mechanical properties of the thixoformed part are close or ever than those of the hot-rolled plate. The high mechanical properties of the thixoformed parts further confirmed the feasibility of short-process thixoforming route

Industrialized Application of Rheo-HPDC Process for the Production of Large Thin-Walled Aluminum Alloy Parts

A simplified and efficient process, namely air-cooled stirring rod (ACSR), was proposed to prepare semisolid slurry of aluminum alloys. An advanced integrated rheological high pressure die-casting (Rheo-HPDC) technology was established by combining the ACSR equipment with HPDC machines to produce high quality aluminum alloy products. Microstructures, surface qualities, mechanical properties, corrosion resistances and thermal conductivities of the Al-8Si alloy parts prepared by Rheo-HPDC were investigated and compared to those prepared by traditional HPDC. The results indicated that the Rheo-HPDC process can prepare aluminum alloy parts in which the primary particles are fine and spherical, and there is few shrinkage porosity. Multifarious high quality large thin-walled aluminum alloy parts, such as filter shells, cooling shells, antenna crates and mounting brackets for communication, were produced by the process. Rheo-HPDC alloys showed improved surface quality to those formed by traditional HPDC, and the surface roughness is small and avoid employing CNC to surface finish. Also, compared with HPDC alloys, the alloys prepared by Rheo-HPDC have an increased mechanical properties and thermal conductivity due to high density and refined microstructure. Furthermore, Rheo-HPDC aluminum alloys indicated a remarkable improvement in corrosion resistance as shown by the results of electrochemical and weight loss experiments.

Metallurgical Structure of A356 Alloy Solidified by Mechanical Stirring

The study investigated the effects of mechanical stirring before solidification on the metallurgical structure of hypoeutectic aluminum-silicon A356. A series of stirring trials were conducted in the present study. Emphasis were placed on the morphological changes of the primary phase, which was subjected to different levels of stirring at various values of the rod material and its diameter, insertion temperature and rotation speed. It was found that when the rod was made of the same material as the molten metal, it acted as a nucleation site to generate numerous nucleated primary crystals, which separated from the rod surface continuously into the molten metal with the rotation of the stirring rod, resulting in the refinement and spheroidization of the primary crystals. The ideal semisolid slurry with homogeneous spherical and fine primary crystals could be obtained by optimizing rod insertion temperature, rotation speed and its diameter, which is a key factor in semi-solid forming.