Explore the vast range of titles available.

In the present work, a novel low-temperature heat-treatable recycled die-cast Al–Mg alloy was developed by adding Zn into non-heat-treatable Al–5Mg–1.5Fe–0.5Mn alloy. The results showed that Zn additions resulted in the formation of equilibrium phase T-Mg 32 (Al, Zn) 49 under as-cast condition, which can be dissolved into the α-Al matrix at a relatively low solution temperature (430 °C) and thus set the base for the low-temperature heat treatment. The mechanical test results indicated that Zn additions had a smooth liner improvement in the strength of all as-cast alloys and T6-state alloys with 1% and 2% Zn as its concentration increased but resulted in a sharp improvement on the strength of T6-state alloy when Zn concentration increased from 2 to 3%. TEM analysis revealed that the precipitate in T6-state Al–5Mg–1.5Fe–0.5Mn–3Zn alloy is η′ phase, rather than the widely reported T″ or T′ phase in other Al–Mg–Zn alloys with approximately same Mg and Zn concentrations. After the optimized low-temperature T6 heat treatment (solution at 430 °C for 60 min and ageing at 120 °C for 16 h), the Al–5Mg–1.5Fe–0.5Mn–3Zn alloy exhibits the yield strength of 321 MPa, ultimate tensile strength of 445 MPa and elongation of 6.2%.

Layered extrusion forming, a type of additive manufacturing technique, was applied in this study, using aqueous ceramic pastes to build near-net-shaped ceramic cores at room temperature. As an example, aqueous-based pastes of alumina using methylcellulose (MC) as binder were prepared, and layered extrusion forming method was employed to fabricate green alumina cores. Afterwards, post sintering was carried out to obtain ceramic cores with high strength. Pastes with alumina solid loading varying from 30 to 52 vol.% were dispersed by MC solutions and presented shear-thinning rheological behaviors. Solid loading had a significant effect on the processing of layered extrusion formation. Alumina pastes with 30 to 46 vol.% were not suitable for layered extrusion formation, while pastes with solid loading ranging from 48 to 52 vol.% could be applied successfully to the layered extrusion forming process. Pastes composed of 2 wt.% MC solution as binder and 50 vol.% solid loading generated specimens with best shape retention and surface consistency, and the height of each layer extruded was equally distributed. The green specimens exhibited slightly smaller dimensions than the designed ones, and sintered specimens showed linear shrinkage. Sintered specimens presented homogeneous morphology, and no gap between extruded filaments was observed. Specimens sintered at 1600 °C for 180 mins possessed best comprehensive performances and low thermal expansion, which could meet the requirements of ceramic cores in alloys casting. The systematic study of layered extrusion forming indicates that this method is a promising method to fabricate ceramic cores.

In the present work, the Al/Mg bimetallic composites were produced using lost foam casting (LFC) process, and the effects of the pouring temperature on the microstructure, mechanical properties, and fracture behavior of the Al/Mg bimetallic composites produced by the LFC process were investigated in order to obtain an optimized bonding between aluminum alloy and magnesium alloy. It was found that the pouring temperature had a significant effect on the interface between the aluminum and the magnesium. With increasing pouring temperature, the thickness of the interface layer obviously increased. When the pouring temperature was 730 °C, a compact and uniform interface layer was obtained between the aluminum and the magnesium. The interface layers of the Al/Mg bimetallic composites obtained with different pouring temperatures primarily consisted of three different reaction layers, namely Al 12 Mg 17  + δ-Mg eutectic, Al 12 Mg 17  + Mg 2 Si, and Al 3 Mg 2  + Mg 2 Si. The interface layers of the Al/Mg bimetallic composites with different pouring temperatures had higher microhardnesses compared to the base metals. The Al/Mg bimetallic composite with the pouring temperature of 730 °C obtained a maximum shear strength due to its superior interface, showing an optimized bonding between the aluminum and the magnesium. The SEM fractograph of the bimetallic composite mostly exhibited a brittle fracture morphology, and the Al 12 Mg 17  + δ-Mg eutectic partly generated a plastic deformation.

A water-soluble salt core (WSSC) strengthened by reinforcing particles, including bauxite powder, glass fiber powder, and sericite powder, was fabricated by gravity-casting process. The surface quality, bending strength, water solubility, humidity resistance, and shrinkage rate of WSSC were investigated, and the synergistic effect between the different reinforcements on the bending strength was analyzed. Scanning electron microscope (SEM) was used to study the micromorphology of WSSC. The results indicate that the binary composite WSSC after being strengthened has excellent comprehensive performance, the bending strength increases by more than 1.4 times with the maximum value of 47.89 ± 0.83 MPa whose 24-h hygroscopic coefficient is lower than 0.18%, the water solubility rate is higher than 163.97 kg/(min m 3 ) in still water at 80 °C, and the shrinkage rate is dramatically lower than that without any reinforced materials; in addition, there are no obvious casting defects on the core surface. The microscopic analysis demonstrates that the homogeneous distribution of the reinforcements in the matrix consumes more energy during the crack propagation procedure and the grain refinement of WSSC is also observed, above which is the main reason for the improvement of the bending strength. Furthermore, the practical casting test of the complex soluble salt core prepared by pressure core making was used for zinc alloy die casting.

The lost foam casting (LFC) process was used to prepare the A356 aluminum and AZ91D magnesium bimetallic castings, and the interface characteristics of the reaction layer between aluminum and magnesium obtained by the LFC process were investigated in the present work. The results indicate that a uniform and compact interface between the aluminum and magnesium was formed. The reaction layer of the interface with an average thickness of approximately 1000 μ m was mainly composed of Al 3 Mg 2 and Al 12 Mg 17 intermetallic compounds, including the Al 3 Mg 2 layer adjacent to the aluminum insert, the Al 12 Mg 17 middle layer, and the Al 12 Mg 17 + δ eutectic layer adjacent to the magnesium base. Meanwhile, the Mg 2 Si intermetallic compound was also detected in the reaction layer. An oxide film mainly containing C, O, and Mg elements generated at the interface between the aluminum and magnesium, due to the decomposed residue of the foam pattern, the oxidations of magnesium and aluminum alloys as well as the reaction between the magnesium melt and the aluminum insert. The microhardness tests show that the microhardnesses at the interface were obviously higher than those of the magnesium and aluminum base metals, and the Al 3 Mg 2 layer at the interface had a high microhardness compared with the Al 12 Mg 17 and Al 12 Mg 17 + δ eutectic layers, especially the eutectic layer.

A new water-soluble calcia-based ceramic core of using epoxy resin binder was developed for investment casting by aqueous gel casting. The influences of dispersant addition and solid loading on the rheological property of the slurries were investigated. The low-shrinkage and high-strength ceramic body was obtained by adjusting binder addition and solid loading. The water-soluble behavior of the calcia-based ceramic core and its solution mechanism were studied. The results show that the 48 vol% slurry composing of 6 wt% dispersant content, 16 wt% binder content, and 20 wt% hardener content can prepare a stable and fluidic slurry, and the bending strength of the dried green body is 29.5 ± 1.4 MPa, the linear shrinkage is 3.62 %, and the green relative density is 58.5 % with a homogeneous microstructure. After sintering at 1300 °C, the ceramic core exhibits a uniform microstructure with a bending strength of 25 ± 1.2 MPa, a sintered shrinkage of 11.31 %, a relative density of 92.3 %, and an apparent porosity of 30.5 %. The solubility rate of the ceramic core is 2.83 kg/min m 2 , and the dissolution of the ceramic core in water is exothermal. The water-soluble calcia-based ceramic core fabricated by aqueous gel casting using epoxy resin could overcome the poor leachability of the common ceramic core and enhanced the production efficiency.

Ultrasonic-assisted plastic micro-forming is a research hotspot in metal-forming process. The friction characteristic is a key factor affecting the micro-forming properties of metal in ultrasonic-assisted micro-forming process. However, the existed researches were mostly focused on the friction characteristics of free surfaces, while few were studied on the friction characteristics between sample and mold cavity. In this paper, the micro double cup extrusion experiments of copper T2 were conducted to investigate the friction characteristics between sample and mold cavity with multiple ultrasonic vibration modes. Furthermore, the numerical model was developed to quantify the friction stress reduction caused by multiple ultrasonic vibration modes and estimate its contribution to decreasing the forming stress, which was usually considered mainly affected by acoustic softening, stress superposition, and friction reduction. The results show that the forming stress and the surface roughness of extruded samples are decreased sequentially with the multiple ultrasonic vibration modes of tool vibration (TV), workpiece vibration (WV), and compound vibration (CV). The cup height ratios of double cup extrusion are also increased sequentially with the ultrasonic vibration modes. But the increase of cup height ratio does not indicate the increase of friction coefficient. The friction stress reduction between sample and mold cavity is increased sequentially with TV, CV, and WV modes, and its contribution to decreasing the forming stress is 48%, 15%, and 49%, respectively.

Silicon carbide (SiC) ceramic material has become the most promising third-generation semiconductor material for its excellent mechanical properties at room temperature and high temperature. However, SiC ceramic machining has serious tool wear, low machining efficiency, poor machining quality and other disadvantages due to its high hardness and high wear resistance, which limits the promotion and application of such materials. In this paper, comparison experiments of longitudinal torsional ultrasonic vibration grinding (LTUVG) and common grinding (CG) of SiC ceramics were conducted, and the longitudinal torsional ultrasonic vibration grinding SiC ceramics cutting force model was developed. In addition, the effects of ultrasonic machining parameters on cutting forces, machining quality and subsurface cracking were investigated, and the main factors and optimal parameters affecting the cutting force improvement rate were obtained by orthogonal tests. The results showed that the maximum improvement of cutting force, surface roughness and subsurface crack fracture depth by longitudinal torsional ultrasonic vibrations were 82.59%, 22.78% and 30.75%, respectively. A longitudinal torsional ultrasonic vibrations cutting force prediction model containing the parameters of tool, material properties and ultrasound was established by the removal characteristics of SiC ceramic material, ultrasonic grinding principle and brittle fracture theory. And the predicted results were in good agreement with the experimental results, and the maximum error was less than 15%. The optimum process parameters for cutting force reduction were a spindle speed of 22,000 rpm, a feed rate of 600 mm/min and a depth of cut of 0.011 mm.

A composite inorganic salt core with good water solubility and formability was proposed using potassium nitrate (KNO3) and potassium chloride (KCl) as base materials. The KNO3–KCl molar ratio has been optimized for the KNO3–KCl composite salt core, and then a low-cost bauxite powder acting as a reinforcing material was added to strengthen the optimized KNO3-KCl composite salt core for the application of hollow zinc alloy die castings. The results show that 70 mol% KNO3-30 mol%KCl composite salt core (CSC) possesses a good comprehensive performance, which has the maximum bending strength of 26.5 MPa and the excellent water solubility rate of 998 g/(min·m2). With increasing the bauxite powder content, the bending strength and vickers hardness of the CSC increase, but the water solubility rate of the CSC decreases gradually. When the bauxite powder content is 30 wt.%, the CSC has a bending strength of 42.99 MPa and vickers hardness of 39.2 HV, which respectively increased by 62.2% and 39.5%, and the water solubility rate is still higher than 692.9 g/(min·m2). The microanalysis reveals that the bauxite powder is stable and evenly distributed among the CSC matrix, which significantly refines the KCl primary phase, resulting in improving the properties of the CSC. Additionally, the crack deflection and branching caused by bauxite powder also enhance the properties of the CSC.

A novel water-soluble sand core hardened by twice microwave heating was fabricated using composite solution of magnesium sulfate and sodium sulfate as a binder. The tensile strength, water absorption rate, gas evolution and water-soluble rate of the water-soluble composite sulfate sand core (WCSSC) were studied. The micro-morphology of WCSSC was observed by scanning electron microscope (SEM). The results show that tensile strength of WCSSC is 1.2 MPa, and the 4 h storage tensile strength exceeds 1 MPa, and also the water-soluble rate is about 42.65 kg/(min m 2 ), which indicates that WCSSC possesses good moisture resistance and water-soluble collapsibility. The microscopic analysis demonstrates that there are some micro-cracks or holes in the bonding bridge that decreases the strength of WCSSC after being put in humidistat for several hours.