A new shell casting process based on expendable pattern with vacuum and low-pressure casting for aluminum and magnesium alloys

A new shell casting process, with the adoption of the foam pattern of lost foam casting (LFC) as prototype and the combination of the thin shell fabrication technology of investment casting and vacuum and low-pressure casting process, was proposed for manufacturing complicated and thin-walled aluminum and magnesium alloy precision castings. Loose-sand uniting vacuum was used in the new process to further reinforce the thin shell, and the new process proves to be a process with simple process, low cost, and high thin shell strength. Because the molten metal filling and solidification are completed under air pressure and vacuum level, the filling capability and feeding capacity of the molten metal are greatly improved, and the castings become denser. This paper mainly investigated the fabrication technology of thin shell based on foam pattern prototype, the removing foam and roasting shell process and vacuum and low-pressure casting process. The few-layer compound thin shell of silica sol–sodium silicate was adopted for the new process. Removing foam pattern was carried out at 250°C for 30 min, and the shell was roasted at 800°C for 1 h. Combined with the vacuum and low-pressure casting process, this new shell casting process has successfully produced thin wall and complex aluminum and magnesium alloy parts with high quality. In addition, comparisons in terms of filling ability, microstructure, mechanical properties, porosity, and surface roughness among this new shell casting, gravity casting, and LFC were also made to show the characterization of this new shell casting process.     

Effect of internal fluid pressure on quality of aluminum alloy tube in rotary draw bending

In the present study, the rotary draw bending of aluminum alloy tubes with internal fluid pressure is investigated by finite element simulation and experiments. The effect of the internal pressure on the cross-section ovality, wall thinning, and wall thickening was studied. The results show that the internal pressure has a significant effect on cross-section quality of aluminum alloy bent tubes. As the internal pressure increases, the cross-section ovality and the wall thickening decrease, and the wall thinning increases. The effect of internal pressure on wall thinning is more significant than its effect on wall thickening.     

Influence of Ti,B and Sr on tribological properties of A356 alloy

Abstract

The wear behaviour of an A356 alloy has been investigated in this paper. To understand the wear behaviour of the materials, the experiments were carried out using a pin on disc testing machine at various combinations of normal pressure, sliding speed and sliding distances. Tribological results reveal that weight loss of A356 alloy increases with increasing normal pressure and decreases with increasing sliding speed. Also, the results at microlevel revealed a structural change from coarse columnar dendrites to fine equiaxed ones on the addition of grain refiner (Al and B) and furthermore, plate-like eutectic silicon to fine particles on addition of modifier (Sr). It is further noted in the present study that addition of modifier does not disturb the influence of grain refiner and vice versa. Abrasive wear mechanism was interrupted by the formation of microwelds and later by oxidation of the Al matrix.     

The effect of solid fraction and indirect forging pressure on mechanical properties of wrought aluminum alloy fabricated by electromagnetic stirring

This study demonstrated the effect of solid fraction and forging pressure on mechanical properties of the product of wrought aluminum alloys fabricated by the indirect rheoforging through electromagnetic stirring (EMS). In addition to EMS, the rheological material was examined for its response to various pouring temperatures as the rheo-material was forged into a sample which consisted parts that were directly and indirectly subjected to forge pressure. As results of investigating the relationship between microstructural features and mechanical properties of the product through microscopic inspection, the EMS rheo-forged materials revealed a fine and globular microstructure. Microstructures of Al6061 wrought aluminum alloy with uniform solid and liquid phase distributions (no segregation) demonstrated good mechanical properties with tensile strengths of up to 341 MPa.     

A study of surface quality and mechanical strength in 5083 aluminum alloy plates using pulsed laser cleaning

In this work, pulsed laser cleaning was conducted on 5083 aluminum alloy plates for removing the oxide film and improving the surface quality. The chroma was innovatively introduced to evaluate the surface quality of cleaned samples. Samples with good cleaning quality were successfully achieved by means of process optimization involving single factor and orthogonal laser cleaning tests. The optimum cleaning parameters for desirable effect consisted mainly of average power of 40 W, scanning speed of 2500 mm/s and repetitive frequency of 85 kHz. On this basis, a well-formed welded joint can be obtained because of the removal of the oxide film on the surface of aluminum alloy. It has been found that the maximum stress and strain of joints subjected to laser cleaning were up to 102.5 % and 114.81 % of joints laser welded in the absence of laser cleaning, respectively. Significant improvement in mechanical strength was mainly attributable to effective suppression of porosities in welds on account of the removal of oxides with the assist of pulsed laser cleaning.

     

Effect of the casting temperature on temperature field and microstructure of A2017 alloy during an innovative continuous semisolid rolling process with a vibrating sloping plate device

In this paper, the effect of temperature field on microstructure of A2017 alloy during an innovative continuous semisolid rolling process with a vibrating sloping plate device was studied. The results show that the alloy temperature decreases gradually from the entrance to the exit of the roll gap. In the backward slip zone, the isothermal lines have twice buckling. In the forward slip zone, the isothermal lines have once buckling. Semisolid region moves forward from the filling mouth to the exit of the roll gap with the increment of casting temperature, and the solid fraction increases from the entrance to the exit of the roll gap. The average grain size of the product increases with the increment of casting temperature, and the plastic deformation along the rolling direction happened obviously. According to the simulation and experiment, the proper casting temperature between 650 and 680 °C is suggested. A2017 alloy strip with good surface quality was obtained. The microstructure of the product is mainly composed of fine spherical or rosette grains which were elongated along rolling direction.