铝/钢电磁脉冲焊接IMCs性能的计算与试验分析

Calculation and experimental analysis of properties of IMCs in electromagnetic pulse welding with aluminum to steel

采用第一性原理计算了铝/钢电磁脉冲焊接极窄焊缝Fe-Al金属间化合物(intermetallic compounds,IMCs)的不同晶面的热力学稳定性、表面能和电子功函数值,并结合界面微观形貌的扫描电子显微镜(scanning electron microscopy,SEM)、X射线衍射(X-ray diffraction,XRD)等测试方法,分析了焊缝可能存在的IMCs及其对界面腐蚀性能的影响.结果表明,第一性原理计算结果与试验数据基本吻合,计算得到铝/钢IMCs形成能和结合能均为负值,且满足热力学稳定结构,其形成能力强弱顺序为Fe_(2)Al_(5),FeAl,FeAl_(3),Fe_(3)Al和FeAl_(2),稳定性强弱顺序为Fe_(2)Al_(5),Fe_(3)Al,FeAl,FeAl_(3)和FeAl_(2),其中Fe_(2)Al_(5)的形成能为-9.379 eV/atom,结合能为-13.612 eV/atom,是焊缝最稳定的相;电子功函数值对应的耐腐性由弱到强顺序为Al,FeAl_(2),FeAl_(3),Fe_(2)Al_(5),FeAl和Fe_(3)Al;能谱仪(energy dispersive spectroscope,EDS)分析表明,焊缝主要存在Fe_(2)Al_(5),FeAl_(3)和少量FeAl_(2),椭圆环形焊缝还存在FeAl,直形焊缝还有Fe_(3)Al;焊缝FeAl_(3)的电子功函数较小,在盐雾腐蚀介质中充当阳极,易被腐蚀,并随着腐蚀周期增长,焊缝主要相Fe_(2)Al_(5)充当阳极,并由直形焊缝向椭圆环形焊缝快速腐蚀扩展,至整条焊缝失效.

The thermodynamic stability,surface energy and value of electronic work function of different crystal planes of intermetallic compounds(IMCs)in an extremely narrow weld with aluminum to steel in electromagnetic pulse welding are calculated using the first principle.Combined with scanning electron microscopy(SEM),X-ray diffraction(XRD),and other testing methods of the interface microscopic morphology,the possible presence of IMCs in the weld seam and its influence on the corrosion property of the interface are analyzed.The results show that the results of first-principle calculation are basically consistent with the experimental data,and the calculated formation energy and binding energy of Al-Fe IMCs are both negative and meet the thermodynamically stable structure,it's the strength of the formation ability as follows Fe_(2)Al_(5),FeAl,FeAl_(3),Fe_(3)Al and FeAl_(2),and its stability is as follows,Fe_(2)Al_(5),Fe_(3)Al,FeAl,FeAl_(3) and FeAl_(2),where the forming energy of Fe_(2)Al_(5) is-9.379 eV/atom,and the binding energy is-13.612 eV/atom,which is the most stable phase in the weld.The corrosion resistance from weak to strong corresponding to the value of electronic work function is as follows Al,FeAl_(2),FeAl_(3) Fe_(2)Al_(5),FeAl and Fe_(3)Al;energy dispersive spectroscope(EDS)analysis shows that Fe_(2)Al_(5),FeAl_(3) and small amounts of FeAl_(2) exist in the weld,there are FeAl in elliptic ring weld,and Fe_(3)Al in straight weld.The value of electronic work function of weld FeAl_(3) is small,which acts as the anode in the salt spray corrosion medium and is easy to be corroded.With the increase of the corrosion period,the main phase of the weld Fe_(2)Al_(5)acts as the anode for rapid corrosion expansion from straight weld to elliptic ring weld,until the whole weld failure.The results provide data reference for controlling the morphology,connection mechanism and corrosion resistance of intermetallic compound in electromagnetic pulse welding with steel to aluminum.