5A06铝合金搅拌摩擦焊接接头的金属流动规律,显微组织以及腐蚀行为研究

Flow law, microstructure and corrosion behavior of friction stir welded 5A06 alloy

摘要:

本文对5A06铝合金在搅拌摩擦焊接过程中的金属流动规律以及焊后显微组织演变和腐蚀行为进行研究。结果表明：由于受到扭转和漩涡运动的综合作用,前进侧金属被直接卷入搅拌针的螺纹内部,然后被向下挤压进入焊核区。然而,后退侧的金属展现出无序的金属流动模式。通过背散射扫描电子显微分析发现,搅拌区的晶粒在动态再结晶的作用下发生了明显的细化,再结晶后平均晶粒尺寸约为6μm。对搅拌区的扫描电子显微分析结果表明,β相(Al₃Mg₂)和Al₆(Mn, Fe)呈弥散分布,且和母材相比Al₆(Mn, Fe)颗粒明显细化。同时,焊缝截面的硬度分布表明焊后5A06铝合金具有软化趋势,最小硬度值为72HV,位于搅拌区和热机影响区的界面处。通过电化学分析和侵泡后的组织观察发现搅拌区的耐腐性明显优于母材,母材的腐蚀电位为-0.725V,而搅拌区域腐蚀电位升高35mV。

Abstract:

The evolution of metal flow, microstructure and corrosion properties of 5A06 alloy after friction stir welding has been studied in present paper. It was observed that metal on the advancing side is curled directly into the threads and then is extruded down into the weld nugget zone by complex motions of torsion and swirl. However, the material on the retreating side encounters chaotic flow patterns. The electro backscattering diffraction results indicated that the grains in stir zone were pronouncedly refined by dynamic recrystallization, the average grain size is about 6μm. The scanning electron microscope analysis displayed that β-phase (Al₃Mg₂) and Al₆(Mn, Fe) dispersedly distribute in the stir zone and the size of the Al₆(Mn, Fe) is smaller than that in base material. The hardness profile is characterized by material softening along the cross-section and the minimum hardness value of 72HV is located in the interface between stirring zone and thermo-mechanically affected zone. It was evident that the stir zone exhibits better corrosion resistance than the base material. The corrosion potential of stir zone is 35mV larger than that in base material (-0.725V).