(1.北京工業(yè)大學(xué)材料與制造學(xué)部，北京 100124；
2.威海萬(wàn)豐鎂業(yè)科技發(fā)展有限公司，威海 264209)
摘 要: 本文基于Clyne-Davies模型評(píng)價(jià)了Mg-xGd-1Er-0.5Zr(x=8.0、10.0、12.0, 質(zhì)量分?jǐn)?shù)，%)合金的熱裂敏感性，并利用“約束桿”鑄造鋼模實(shí)驗(yàn)方法驗(yàn)證了該合金的熱裂傾向。結(jié)果表明基于Clyne-Davies模型得到的計(jì)算結(jié)果能有效預(yù)測(cè)Mg-xGd-1Er-0.5Zr合金熱裂敏感性，且隨著Gd含量的增加，合金的熱裂敏感性下降。采用數(shù)據(jù)采集系統(tǒng)、電子顯微鏡及X射線衍射儀等手段，對(duì)鑄件凝固曲線、微觀組織和析出相進(jìn)行了分析，發(fā)現(xiàn)隨著Gd含量的增加，合金的熱裂敏感性降低，其原因是凝固后期Mg5(Gd，Er)共晶液相的增多有利于枝晶間裂紋的補(bǔ)縮。此外，共晶液相也會(huì)抑制α-Mg枝晶的形核長(zhǎng)大，使合金的凝固溫度區(qū)間減小，從而降低合金的熱裂敏感性。對(duì)熱裂斷口進(jìn)行分析后認(rèn)為，斷口出現(xiàn)的液膜以及晶間搭橋提高了晶間結(jié)合力，這是熱裂敏感性降低的另一個(gè)重要原因。
關(guān)鍵字: Mg-Gd-Er-Zr合金；凝固；微觀組織；熱裂模型；熱裂敏感性
（1.Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China;
2.Weihai Wanfeng Auto Holding Group Co., Ltd.,Weihai 264209, China）
Abstract:Hot tearing is a potential problem that deteriorates the ductility of Mg castings. The effects of Gd content on the hot cracking susceptibility (H) of Mg-xGd-1Er-0.5Zr (x=8.0, 10.0, 12.0, mass fraction, %) were predicted based on the Clyne-Davies model, and verified by using the “constraint rod” permanent mold test. The results show that the variation of H value of the Mg-xGd-1Er-0.5Zr alloys can be effectively predicted by the Clyne-Davies model and the theory values are in consistent with the experimental ones. The microstructure and the precipitates in the as-cast Mg alloys were analyzed by scanning electron microscopy (SEM) and X-ray diffractometery (XRD). It is demonstrated that the H value decreases with the increase of Gd content.The higher Gd contents lead to the increase of the volume fraction of Mg5(Gd, Er) eutectic phase, which is facilitated to feed the micro-cracks between the dendrite arms during the terminal solidification stage, so as to decrease the H value. In addition, the eutectic phase also inhibits the nucleation and growth of α-Mg dendrites and thus reduces the solidification temperature range of the alloy. Combined with the fracture surface observation, it is suggested that the liquid film and bridgebetween the grains during solidification improvethe grain-binding force, which is also considered as another important reason responsible for reducing the H value.
Key words: Mg-Gd-Er-Zr alloy; solidification; microstructure; hot tearingmodel; hot cracking sensitivity
