Investigation of carbon contamination in lost foam castings of low carbon steel

Lost foam casting(LFC) process is a special casting method in which polymeric foam patterns with refractory coatings are utilized as a mould component. In this work, four types of foam: expandable polyethylene(EPE), expandable polypropylene(EPP) and expandable polystyrene(EPS) foams with two different densities were employed as pattern materials. LFC and conventional green sand mould casting methods were used to cast a low carbon steel, A216 Grade WCB. Both casting processes were carried out at 1,580 °C. Chemical analysis results showed that the carbon contamination level was high and was influenced by pattern type. Metallographic investigations revealed a significant increase in the percentage of pearlite phase in all LFC samples. Densities of manufactured samples were calculated in order to evaluate porosity of the products. It was determined that the densities of the LFC samples were lower than the green sand mould cast reference sample(RS). Vickers hardness tests were also carried out and increments in hardness values with increased carbon content was observed.

Influence of solution treatment on microstructure, corrosion resistance, and oxidation behavior of cast G-NiCr28W alloy

G-NiCr28W is a nickel-based cast alloy. Its microstructure consists of nickel-rich matrix phase and chromium-rich eutectic carbides. The solution treatment process can provide homogenous microstructure and desired mechanical/thermal properties for G-NiCr28W alloy. However, the solution treatment process affects the corrosion resistance of the alloy and it causes metal loss due to the occurrence of oxidation at atmospheric conditions. Therefore, determining the changes in the properties of the G-NiCr28W is important. For this purpose, G-NiCr28W specimens were solution treated at 1,040 ℃, 1,100 ℃ and 1,160 ℃ for 1 h and 8 h, respectively. The microstructures of the solution-treated samples were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. Moreover, hardness, corrosion resistance and oxidation behaviors of the solution-treated samples were examined. The solution treatment process applied at 1,160 ℃ led to the formation of Fe_2W_2C blocky carbides, and hardness of the sample increased with the existence of blocky carbides, while corrosion resistance decreased. Furthermore, excessive metal loss occurred depending on oxidation due to the high process temperature at 1,160 ℃.

T6热处理对触变锻造加低过热铸造制备的A356和A380铝合金的影响（英文）

研究T6热处理对触变锻造A356和A380铝合金的影响。采用低过热铸造(LSC)技术制备用于触变锻造的样品。为了获得等轴晶粒并防止枝晶生长,将样品在高于液相温度20°C时进行浇铸,将浇铸坯料再加热不同时间(20~80 min)后进行触变锻造,变形量为50%,再将触变锻造后的A356和A380铝合金样品进行T6热处理。用光学显微镜、能量弥散X射线谱仪、扫描电镜和布氏硬度仪对经触变锻造、固溶处理和时效处理后样品的显微组织和硬度变化进行检测。结果表明,T6热处理后合金的显微组织更均匀,并分别在A356和A380坯料中形成了新的析出相Mg_2Si和Al_2Cu。相应地,经过人工时效后,样品的硬度大幅度提高,A356铝合金的硬度达到HB 93,A380铝合金的硬度达到HB 120。

冷却倾斜板铸造、再加热和触变锻造AA7075铝合金（英文）

冷却倾斜板铸造已成功应用于生产非枝晶组织铝合金的铸造中。为了研究半固态铸造对AA7075铝合金显微组织的影响,用冷却倾斜板浇铸法制备具有非枝晶组织的AA7075铸锭,并对其进行再加热和触变锻造。对铸件进行金相观察、图像分析、扫描电镜和能谱分析。组织分析结果显示,材料的晶粒尺寸和球形度较好。在再加热过程中,晶粒可能突然变粗。冷却倾斜板铸造采用30°和60°倾斜角,采用60°倾斜角的结果更好。此外,短时再加热和半固态锻造致使固态晶粒中微量元素析出。

真空辅助熔模铸造制备A6063/SiC-B_4C混杂复合材料(英文)

采用真空辅助熔模铸造技术制备A6063/SiC-B4C混杂复合材料。首先,采用平均粒径分别为60μm和55μm、质量比为85%和15%的SiC和B4C粉末制备圆柱形的SiC-B4C预制块。然后,将预制块放入圆柱形石膏粘结块熔模中,在真空辅助铸造机中将A6063铝熔体浸渗到预制块中。采用阿基米德方法测定预制块中的孔隙度。对制备的复合材料进行硬度测试、图像分析、SEM观察和EDX成分分析。结果表明,采用真空辅助熔模铸造技术,铝熔体能将够成功地浸渗到预制块中。