Abstract

When alloys are exposed to elevated temperatures they experience a decrement in their mechanical properties that leads to material failure. However, the use of thixoforming, an alternative metal processing method, could enhance mechanical properties by minimising the defects that exist in as-received alloys. Therefore, this study aimed to determine the tensile strength of thixoformed A319 under elevated temperatures by taking into account its intended use in vehicle cylinder head components. Thixoformed A319 was compared with as-received alloy manufactured by permanent mould casting. The cooling slope method was used to prepare the feedstock for thixoforming. The feedstock was reheated by induction heating until it reached 574 °C and was then formed in a mould. Afterwards, the as-received and thixoformed samples underwent T6 heat treatment. The resulting samples were characterised by using optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray, X-ray diffraction analysis and a tensile test. Elevated temperature tensile tests were performed at 250 °C, in line with the temperature condition experienced by cylinder head components during operation. The ultimate tensile strength of the thixoformed samples was 30% higher than that of the as-received samples under elevated temperatures. Also, the analyses of the fracture surfaces showed that porosity, intermetallic compounds and impurities were amongst the failure factors for both alloys.

Graphic Abstract

摘要

当合金暴露于高温下时，它们的机械性能会下降，从而导致材料失效。但是，使用触变成型（一种替代性的金属加工方法）可以通过最大限度地减少原样合金中存在的缺陷来增强机械性能。因此，本研究旨在通过考虑其在车辆汽缸盖组件中的预期用途来确定触变A319在高温下的拉伸强度。将触变成形的A319与通过永久铸模生产的原样合金进行了比较。冷却斜率法用于制备触变性成型的原料。通过感应加热将原料重新加热直到其达到574℃，然后在模具中形成。之后，对接收到的触变性样品进行T6热处理。通过使用光学显微镜，配备能量色散X射线的扫描电子显微镜，X射线衍射分析和拉伸试验对所得样品进行表征。高温拉伸试验是在250°C下进行的，与气缸盖组件在运行过程中所经历的温度条件一致。触变性样品在高温下的极限抗拉强度比原样高30％。同样，对断裂表面的分析表明，孔隙率，金属间化合物和杂质是两种合金的破坏因素之一。高温拉伸试验在250°C下进行，与气缸盖组件在运行过程中所经历的温度条件一致。触变性样品在高温下的极限抗拉强度比原样高30％。同样，对断裂表面的分析表明，孔隙率，金属间化合物和杂质是两种合金的破坏因素之一。高温拉伸试验在250°C下进行，与气缸盖组件在运行过程中所经历的温度条件一致。触变性样品在高温下的极限拉伸强度比原样高30％。同样，对断裂表面的分析表明，孔隙率，金属间化合物和杂质是两种合金的破坏因素之一。

图形摘要