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When the die cycle dwell time was greater than 290


seconds, the extended metal-mold constraint time tended to create more severe hot tearing. Te microstructure image in Fig. 6 shows the progression of hot tearing. Maintaining a die cycle dwell time of 200-230 seconds and maintain- ing the mold temperature between 860-896F (460-480C) provided the best results. Increasing the mold’s tempera- ture above 896F (480C) tended to lead to mechanical hot cracking due to ejection stresses. Te casting trials performed at the partner foundry using the production tooling designed to be used with A356 were successful. Many of the A206 castings were free of hot tearing. Unetched microstructures showed minimal shrinkage defects associated with poor feeding during solidification (Fig. 7). Additionally, the sections A and B showed relatively fine grain structure in etched samples (Fig. 8). Tere appears to be minimum and maximum mold


temperatures allowed in particular areas of the mold (related to casting design) to prevent hot tearing. High spikes in mold temperature in locations close to hot spots in the mold can result in casting breakage during ejection. But reducing hot tearing is possible through effective thermal management. Properly locating temperature sensors and controlling heating and/or cooling in casting hot spots can reduce conditions that lead to hot tears. Additionally, proper grain refinement and control of cast- ing cycle times can minimize hot tears. Simulation and computer modeling programs can help


streamline design efforts and identify potential problem areas, including those that could lead to hot tearing. While this study was able to produce quality castings, more research must be done. Tis project could lay a foundation for future work on developing appropriate charge material and primary/scrap ratio for A206. Achieving that goal will make the casting of alloy 206 in permanent molds more economically viable, which then will lead to wider accep- tance within the metalcasting industry. 


Tis article was based on the presentation “Permanent Mold Cast- ing of a Structural Component from Al Alloy 206” from the 2014 Metalcasting Congress in Schaumburg, Ill.


度、破裂减少,工程师将冷却水流速度调到最大。 在金属型内停留周期超过290秒时,延长了金属铸 型之间的约束时间,可能产生更严重的热裂。图6的 微观结构图显示了热裂的形成过程。将铸型内停留周 期保持在200-230秒,型温保持在860-896F (460- 480C)之间,可以得到最好的效果。铸型的温度达到 896F (480C)以上时,将有可能因顶压离型的应力产 生机械作用的热裂。


在合作伙伴的铸造厂,采用为A356合金设计的工 艺装备进行的铸造试验获得了成功。很多A206合金 铸件都没有产生热裂。未经浸蚀的试样微观结构表 明,凝固过程中由于补缩较差引起的收缩缺陷最小( 图7)。此外,A和B两部位的浸蚀样品表明晶粒的结 构比较细小(图8)。


在铸型的特定位置(与铸件设计有关),金属型 能适应的最低和最高温度似乎可以防止产生热裂。热 节附近的型温达到峰值,可能导致铸件在顶压离型过 程中破裂。但是,可以通过有效的热管理减少热裂。 正确地安放温度传感器、控制好铸件热节区域的加热 和/或冷却,可以减少热裂的产生。此外,适当的晶 粒细化和铸造周期控制,可以将产生热裂的可能性降 到最低。


模拟技术和计算机建模项目有助于简化设计工作, 确定潜在的问题部位,包括可能导致产生热裂的部 位。虽然此项研究工作有助于生产高质量的铸件,但 还需进行更多的研究。该项目将为今后A206合金选 取适用的装炉材料和原材料/回炉率配比奠定基础。目 标实现后,将使金属型铸造A206合金件变得更加经 济,从而使它在铸造行业中的应用更为普遍。


本文以在伊利诺伊州绍姆堡举办的2014年美国铸造大会 上发表的“206铝合金结构铸件的金属型铸造工艺”为基 础。 


Fig. 8. The distribu- tion of shrinkage in an etched micro- structure sample is shown.


图8:经浸蚀的微 观结构试样的缩 松分布情况。


March 2015 FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 45


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