(1. 上海大學(xué) 材料基因組工程研究院，上海 200444；
2. 上海大學(xué) 材料科學(xué)與工程學(xué)院，上海 200444；
3. 上海大學(xué) 省部共建高品質(zhì)特殊鋼冶金與制備國(guó)家重點(diǎn)實(shí)驗(yàn)室，上海 200444)
摘 要: 以純鎂為細(xì)化對(duì)象，研究Al-2.8Nb-0.3B(中間合金)作為晶粒細(xì)化劑對(duì)鑄態(tài)純鎂微觀組織、拉伸變形及斷裂行為的影響。結(jié)果表明：隨著中間合金的添加量由0增加至7.14%，晶粒由毫米級(jí)的柱狀晶細(xì)化至平均直徑約196 μm的等軸晶，最大拉伸應(yīng)力由53.8 MPa提升至185.4 MPa，滑移線的平均間距由17.9 μm減至1.3 μm。純鎂經(jīng)7.14%中間合金細(xì)化后的拉伸斷裂過(guò)程與細(xì)化前的存在顯著區(qū)別：細(xì)化前，晶粒內(nèi)部首先產(chǎn)生滑移線，隨后裂紋在最深的滑移臺(tái)階處萌生、擴(kuò)展，并最終斷裂；細(xì)化后，晶粒內(nèi)部同樣先產(chǎn)生滑移線，但隨后裂紋沿晶界處的第二相β-Mg17Al12萌生裂紋和擴(kuò)展，直至最終斷裂。純鎂經(jīng)7.14%中間合金細(xì)化后，合金發(fā)生顯著的細(xì)晶強(qiáng)化，但細(xì)化后合金晶界處形成數(shù)十微米的β-Mg17Al12相，降低了合金的延展性。
關(guān)鍵字: 純鎂；Al-Nb-B細(xì)化劑；微觀組織；原位拉伸；斷裂機(jī)理
（1. Materials Genome Institute, Shanghai University, Shanghai 200444, China;
2. School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China;
3. State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200444, China）
Abstract:Using pure magnesium as the refinement object, the effects of Al-2.8Nb-0.3B master alloy as a grain refiner on the microstructure, tensile deformation and fracture behavior of as-cast pure magnesium were studied. The results show that, when the addition of Al-2.8Nb-0.3B master alloy increases from 0 to 7.14%, the grains are refined from millimeter-lever columnar crystals to equiaxed crystals with an average diameter about 196 μm, and the maximum tensile stresses increase from 53.8 MPa to 185.4 MPa, and the average spaces of adjacent sliding lines reduce from 17.9 μm to 1.3 μm. The tensile fracture behaviors are evidently different before and after the refinement with Al-2.8Nb-0.3B master alloy of 7.14%. Before refinement, the slip lines first appear inside grains, followed by the nucleation and propagation of a crack along the deepest slip step, and then, the crack rapidly leads to fracture. After refinement, the slip lines also appear inside grains first, but then, a crack nucleates and propagates at the second phase β-Mg17Al12, which is mostly located at the grain boundaries. The pure Mg is refined by 7.14% master alloy remarkably, the β-Mg17Al12 second phase with size of roughly tens of microns forms at grain boundry of refined alloy, and the ductility of refined ingot decrease.
Key words: pure Mg; Al-Nb-B grain refiner; microstructure; in-situ tensile; fracture mechanism
