Wettability enhancement of SiCp in cast A356/SiCp composite using semisolid process

The effects of SiCp treatment and magnesium addition on microstructural and mechanical properties of Al356/20 wt% SiCp semisolid composites were investigated. The results showed that cleaning and oxidizing of SiCp and addition of 1 wt% Mg resulted in improving wettability, incorporation, and uniform distribution of SiCp in A356 matrix. Consequently, the ultimate tensile strength (UTS) value increased by 19% and 32% when the SiC was treated and also when Mg was added, respectively, compared to as-received SiCp. In addition, hardness value increased from 69.7 HV in as-received SiCp to 94.8 HV after SiCp treatment and addition of Mg

Effect of bismuth on microstructure of unmodified and Sr-modified Al-7Si-0.4Mg alloys

The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions. The results show that bismuth has a refining effect on the eutectic silicon and its refinement behavior increases with increasing Bi content up to 0.5 (mass fraction). When bismuth is added into the molten alloy modified with strontium, a higher Sr/Bi mass ratio of at least 0.45 is required to attain full modification of the eutectic silicon

A novel method to enhance the performance of an ex-situ Al/Si-YSZ metal matrix composite

A novel technique was used to synthesise an Al–Si/YSZ composite with improved bonding strength between the matrix and YSZ particles. Based on thermal analysis results, Bi was added in slurry state at 605 ± 5 °C, and two-step stirring was applied. It was found that the duration of mushy zone decreased and solidification rate increased with the addition of YSZ particles. Elemental mapping analysis on etched and deep-etched conditions revealed that these YSZ particles were surrounded by Bi. Mechanical characterisation showed that YS, UTS, El% and the hardness of the A356 + Bi/YSZ composite increased by 25.5%, 2%, 43% and 24% respectively. Fractography analysis confirmed that the interfacial bonding strength at Al/YSZ improved significantly with the addition of Bi. The wear rate and friction coefficient of A356 + Bi/YSZ decreased to 0.464 and 0.55 mm3/Km respectively, which are 34.6% and 6.7% lower than the values obtained for the A356/YSZ composite. The worn surface revealed mild abrasion wear mechanisms in the A356 + Bi/YSZ composite

In-situ melting assessment of AZ91D granules by thermal analysis

In this research, the response of AZ91D granules during In-Situ melting as a novel technique for investment casting of magnesium alloy was investigated. In order to assess the melting behaviour, the granules were heated at 700 °C for 30 min under three different protective environments, including covering flux, argon atmosphere and their combination. Thermal analysis experiments were carried out to disclose the heating profile of the granules and to detect any probable characteristic temperatures. Visual analysis was employed to characterize the products of the In-Situ melting process in each environment. The results showed that the granules underwent a severe oxidation when heated under the covering flux solely. However, the detected characteristic temperatures revealed that they experienced melting process during heating although they failed to produce a molten metal pool. Flowing argon gas not only prevented the granules from oxidation suffering, also assisted them to provide molten metal. It was further observed that using covering flux remarkably contributed to an increase in the feasibility of the granules melting in an argon atmosphere

Influence of heat treatment on properties of hot isostatically pressed turbine blade superalloy IN738

Impact of heat treatment on hot isostatically pressed (HIP) Ni-base superalloy has been investigated before and after conducting HIP process. HIP was performed by applying a stress of 120 MPa at a temperature of 1200 °C for 2 hours under argon atmosphere followed by furnace cooling to room temperature. Heat treatment cycle was conducted on the samples according to GEB50A563. Microstructural observation demonstrated the deleterious change of ?' morphology after HIP process which causes to decrease of hardness and creep strength. However, pre heat treatment in compared with cast specimen show slight changes in microstructure but, post heat treatment can revert this change of ?' morphology completely and also increase the mechanical properties

Effect of Wettability Enhancement of SiC Particles on Impact Toughness and Dry Sliding Wear Behavior of Compocasted A356/20SiCp Composites

In this study, the effect of wettability improvement of SiCp on the impact and sliding wear behavior of A356/20 wt% SiCp composites produced by a compocasting technique has been investigated. The result showed an increase of incorporation and uniform distribution of SiCp in the A356 matrix by elimination of SiCp segregation. Desired bonding between SiCp and the aluminum matrix due to improved wettability resulted in enhanced properties in terms of improved impact toughness and wear resistance. This improvement was also associated with partial refinement of coarse eutectic silicon due to increased incorporation and distribution of SiCp reinforcements. The highest enhancement was obtained when 1% Mg was added into the melt in addition to pretreated SiCp. The impact toughness value increased by 10 and 26% and the wear rate decreased by 5 and 30% when the SiC was treated and when Mg was added, respectively, compared to as-received SiCp. The impact fracture surfaces showed fewer decohered and well-bonded SiC particles in A356–(SiC-treated-Mg) composite. The highest wear resistance of A356/SiCp composites was achieved by A356–(SiC-treated-Mg) composite for applied loads of 10 and 20 N compared to other fabricated composites. The worn surface revealed mild abrasion and adhesion wear mechanisms

Evaluation of cutting force and surface roughness in the dry turning of Al-Mg2Si in-situ metal matrix composite inoculated with bismuth using DOE approach

Al-Mg2Si particulate metal matrix composites (PMMC) has recently received wider attention because of its improved properties, however there is a lack of knowledge about machinability characteristics of these composites especially with bismuth addition. The purpose of this study is to evaluate the machining parameters and modifier element effects on cutting force (Fc) and surface roughness (Ra) when dry turning Al-Mg2Si with a coated carbide tool (K10U). The experimental trials are designed using the multi-level factorial design (DOE) and their results are analyzed using Analysis of Variance (ANOVA). Statistical models are developed to represent the relationship among machining parameters as independent variables, surface roughness and cutting force as response variables. For each experiment, a new cutting insert is used to encourage accurate reporting of the cutting force and surface roughness. The statistical observation revealed that the main effect of cutting speed, feed rate and modifier element influenced the cutting force and surface roughness. Moreover, there are no interaction effects of variables. Built-up-edge (BUE) formation was observed at every combinations of cutting speed and feed rate which affected the surface quality negatively. The proximity of predicted results and experimental results provide evidence that the DOE method has successfully derived the predictive models. The addition of Bi as modifier reagent results in lower cutting force and better surface roughness due to the formation of Bi compound and modifies the morphology of Mg2Si reinforcement particle. Our findings showed that the Bi is a promising element to improve the machinability of Al-Mg2Si composite

Evaluations of antimony and strontium interaction in an Al-Si-Cu-Zn die cast alloy

The interaction between antimony and strontium in an ADC12 die casting alloy is investigated comprehensively by using a computer aided cooling curve thermal analysis coupled with microstructure inspection. The results of the thermal analysis show significant changes in Al-Si eutectic reaction based on different concentrations of Sb and Sr. Sb reduces the efficiency of Sr in modifying the eutectic Si. Based upon the data obtained in this study, the threshold Sr/Sb ratio should exceed about 0.5 in order to obtain fully modified structure. Moreover, a pre-eutectic reaction of Al2Si2Sr intermetallic was detected for high concentrations of Sr

Cooling curve thermal analysis of Al–Mg2Si–Cu–xSr composite

In situ composites are today being considered for industrial use, owing to the fewer production steps involved, lower production cost, and better wetting of reinforcements. This study emphasises the characteristic features of an Al–Mg2Si–Cu in situ composite, with the addition of different amounts of Sr (0.01–0.1 mass%) as a modifier reagent, by employing computer-aided cooling curve thermal analysis. The identification of microstructures and phases was carried out using a scanning electron microscope equipped with an energy dispersive spectrometer. The results show that the nucleation temperature of the primary Mg2Si, eutectic Mg2Si, and Al5FeSi phases initially increased with the addition of 0.01 mass% Sr, and subsequently decreased with further addition of the element. Two new Sr-containing phases were detected after the precipitation of primary Mg2Si phase and prior to the formation of eutectic Mg2Si phase. A relationship between the cooling rate (CR) and solidification rate (SR) was established. Based on cell coherency point, it was found that the eutectic Al–Mg2Si cell required a longer time to grow with the increment of Sr. The solid fraction of Al5FeSi and Al5Cu2Mg8Si6 + Al2Cu phases remained constant at 8 ± 1% and 3 ± 1%, respectively. The increase in the terminal freezing range and the cracking susceptibility coefficient, by 182% and 16%, respectively, shows that Sr increases the probability of hot tearing