Doty Herbert W, Samuel Ehab, Samuel Agnes M, Songmene Victor, Samuel Fawzy H
Materials Technology, General Motors Global Technology Center, Warren, MI 48092, USA.
Département des Sciences Appliquées, Université du Québec à Chicoutimi, Saguenay, QC G7H 2B1, Canada.
Materials (Basel). 2025 Feb 26;18(5):1024. doi: 10.3390/ma18051024.
The present study was performed on real-life I4-aluminum cylinder heads produced industrially by applying the lost foam technique to Al-Si-Mg alloys (356 and 357). This work, in addition, introduces a new Al-Cu alloys coded 220 alloy. The main aim of this study is to analyze the effects of liquid metal treatment on the hardness and tensile properties of such castings. The effects of liquid metal treatment (modification with 200 ppm Sr, grain refining with 150 ppm B and degassing using pure Ar) of the castings produced by the lost foam technique on the tensile strength and hardness properties were evaluated. Hydrogen plays an important role in the formation of porosity. At the same time, the foam mold leaves an impression on the casting surface taking the shape of fine holes. In addition, segregation of hydrogen occurs in front of the solidification front. Thus, the porosity is a combination of hydrogen level and the solidification rate. Gains of 17% and 24% are observed for the hardness and yield strength for alloy 357 compared to alloy 356, caused by the difference in their magnesium (Mg) contents in the sense that, in the T6 heat-treated condition, precipitates in the form of ultra-fine MgSi phase particles are formed. The enhancement in the mechanical properties of the used alloy depends mainly of the volume fraction of the precipitated MgSi particles. The hardness of alloy 220 increases by 18% and the yield strength by 15% compared to that measured for alloy 356. In this case, the hardening phase AlCu is responsible for this increase. Thus, this study demonstrates that liquid metal treatments significantly enhance the hardness and yield strength of Al-Si-Mg and Al-Cu alloys, with the gain attributed to refined microstructures and reduced porosity.
本研究是对通过熔模铸造技术应用于Al-Si-Mg合金（356和357）工业生产的实际I4型铝制气缸盖进行的。此外，这项工作还引入了一种新的编码为220合金的Al-Cu合金。本研究的主要目的是分析液态金属处理对这类铸件硬度和拉伸性能的影响。评估了熔模铸造技术生产的铸件经液态金属处理（用200 ppm Sr变质、用150 ppm B细化晶粒和用纯Ar除气）后对拉伸强度和硬度性能的影响。氢在气孔形成中起重要作用。同时，泡沫模具会在铸件表面留下呈细孔形状的印记。此外，氢在凝固前沿前发生偏析。因此，气孔率是氢含量和凝固速率的综合结果。与合金356相比，合金357的硬度和屈服强度分别提高了17%和24%，这是由于它们镁（Mg）含量的差异，即在T6热处理条件下，会形成超细MgSi相颗粒形式的析出物。所用合金力学性能的提高主要取决于析出的MgSi颗粒的体积分数。与合金356相比，合金220的硬度提高了18%，屈服强度提高了15%。在这种情况下，硬化相AlCu导致了这种提高。因此，本研究表明，液态金属处理显著提高了Al-Si-Mg和Al-Cu合金的硬度和屈服强度，其提高归因于细化的微观结构和降低的气孔率。
