Mechanical and Thermal Expansion Properties of SiCp/ZAlSi9Mg Composites Produced by Centrifugal Casting

Centrifugal casting was applied to produce cylindrical castings using SiCp/Al composite slurry,which contained 20%SiC particles.The castings comprised a particle free zone and a particle rich zone.The amount of SiC particles had a dramatic transformation from the particle rich zone to the particle free zone,and the maximum content of SiC particles in the particle rich zone reached up to 40 vol%.The ultimate tensile strength（UTS） of the as-cast SiCp / Al composites in the particle rich zone was 143 MPa,and the fracture was caused by the desorption of SiC particles from matrix alloy.The coefficient of thermal expansion（CTE） of the SiC_p / Al composites in the range of 20 and 100 ℃ was determined as 16.67×10^（-6） s^（-1）,and the experimental CTE was lower than the predicted data based on the Kerner＇s model.The results show that the decrease in CTE in the case of the composites at high temperature stage can be attributed to the solute concentration of Si in Al and the plastic deformation of the matrix alloy in the composites with void architecture.

Evaluation of the microstructure, secondary dendrite arm spacing, and mechanical properties of Al–Si alloy castings made in sand and Fe–Cr slag molds

The microstructure and mechanical properties of as-cast A356（Al–Si） alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome（Fe–Cr） slag, and a mixture of sand and Fe–Cr. A sodium silicate–CO_2 process was used to make the necessary molds. Cylindrical-shaped castings were prepared. Cast products with no porosity and a good surface finish were achieved in all of the molds. These castings were evaluated for their metallography, secondary dendrite arm spacing（SDAS）, and mechanical properties, including hardness, compression, tensile, and impact properties. Furthermore, the tensile and impact samples were analyzed by fractography. The results show that faster heat transfer in the Fe–Cr slag molds than in either the silica sand or mixed molds led to lower SDAS values with a refined microstructure in the products cast in Fe–Cr slag molds. Consistent and enhanced mechanical properties were observed in the slag mold products than in the castings obtained from either sand or mixed molds. The fracture surface of the slag mold castings shows a dimple fracture morphology with a transgranular fracture nature. However, the fracture surfaces of the sand mold castings display brittle fracture. In conclusion, products cast in Fe–Cr slag molds exhibit an improved surface finish and enhanced mechanical properties compared to those of products cast in sand and mixed molds.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.

Effects of Processing Technologies on Mechanical Properties of SiC Particulate Reinforced Magnesium Matrix Composites

Mg matrix composites with SiC particles ranging from 5vol%-25vol% were prepared using stirring casting method. Die casting, squeezing casting, and extrusion were applied for inhibiting or eliminating the defects such as gas porosity and shrinkage void. Through die casting and squeezing casting, most of the defects in Mg matrix composites could be eliminated, but the mechanical properties were improved limitedly. On the other hand, after hot extrusion, not only most of the defects of as-cast composites ingots were eliminated, but also the mechanical properties were improved markedly. With the addition of SiC, the tensile strength, yield strength and elastic modulus of as extrusion SiCp/AZ61 composites increased remarkably, and the elongation decreased obviously.

Microstructure and Mechanical Behavior of Squeeze Cast SiC_w/AZ91 Magnesium Matrix Composites

The interfacial microstructure and tensile properties of the squeeze cast SiCw/AZ91 Mg composites were characterized. There exist uniform, line and discrete MgO particles at the interface between SiC whisker and magnesium in the composites using acid aluminum phosphate binder. The interfacial reaction products MgO are beneficial to interfacial bonding between SiCw and the Mg matrix. resulting in an improvement of the mechanical properties of the composite.

Effects of the precipitation of stabilizers on the mechanism of grain fracturing in a zirconia metering nozzle

The mechanism of grain fracturing in a zirconia metering nozzle used in the continuous casting process was studied. The phase composition, microstructure, and chemical composition of the residual samples were studied using an X-ray fluorescence analyzer, scanning electron microscope, and electron probe. Results revealed that the composition, structure, and mineral phase of the original layer, transition layer, and affected layer of the metering nozzle differed because of stabilizer precipitation and steel slag permeation. The stabilizer MgO formed low-melting phases with steel slag and impure SiO2 on the boundaries（pores） of zirconia grains; consequently, grain fracturing occurred and accelerated damage to the metering nozzle was observed.

A Review on Casting Magnesium Alloys： Modification of Commercial Alloys and Development of New Alloys

The research and development status of casting magnesium alloys including the commercial casting alloys and the new types casting alloys are reviewed,with more attention to microstructure and mechanical properties of modified-AZ91,AM60 and WE43 alloys with various additions,and new types of low cost casting alloys and high strength casting alloys.The modification and/or refinement of Mg2 Si phase in Mg-Al-Si based casting alloys by various additions are discussed and new purifying technologies for casting magnesium alloys are introduced to improve the performance.The modified AZ81 alloy with reduced impurities is found to have the tensile strength of 280 ± 6 MPa and elongation of 16% ± 0.7%.The fatigue strength of AZ91 D alloy could be obviously improved by addition of Ce and Nd.The Mg-16Gd-2Ag-0.3Zr alloy exhibits very high tensile and yield strengths（UTS：423 MPa and YS：328 MPa）;however,its elongation still needs to be improved.