摘要
The effect of T6heat treatment on the fracture strength and reliability of AM60B alloy was studied.The tensile specimens were poured at three different temperatures of670,685and700?C for different holding times of5,10and15min.The fluidity test was also conducted to determine the fluidity length under different pouring temperatures and holding times.According to the results,the optimum pouring temperature and holding time were determined as685?C and10min,respectively.SEM fractography of the tensile specimens reveals that the entrained oxides and oxide-related porosities are the main factors responsible for the reduction of fracture strength under the non-optimal casting conditions.The Weibull statistical approach was used to quantify the scatter of fracture strength in as-cast and heat-treated conditions.For this purpose,T6schedule was applied to the specimens prepared under the optimal casting condition.It is found that,despite minor effect on the average fracture strength,T6heat treatment improves the reliability of castings,where the Weibull modulus is increased by75%.According to the microstructural and fractography observations,this improvement is related to the evolution of more uniform microstructure and the elimination of coarse brittleβ-particles in heat-treated samples.
研究T6热处理对AM60B合金断裂强度和可靠性的影响。在浇铸温度分别为670、685和700?C,保温时间为5、10和15 min条件下,制备拉伸试样。用流动性试验测试了合金在不同浇铸温度和保温时间条件下的流动长度。结果表明,最佳的浇铸温度和保温时间分别为685?C和10 min。拉伸试样的SEM断口形貌分析结果显示夹杂的氧化物和与氧化物相关的孔隙是非优化浇铸条件下断裂强度降低的主要因素。将最佳铸造条件下制备的样品采用T6热处理制度进行热处理,然后用Weibull统计法确定浇铸和热处理条件下断裂强度的分散性。结果表明,T6热处理制度尽管对平均断裂强度影响较小,但是提高了铸件的可靠性,其Weibull模量提高了75%。显微结构和断口形貌的观察结果显示,热处理后样品的显微组织更加均匀,且消除了粗大的脆性β相颗粒,从而提高了铸件的性能。
