微量Co对7056铝合金组织与腐蚀性能的影响

Effect of Trace Co on Microstructures and Corrosion Properties of 7056 Aluminum Alloy

通过金相观察、晶间腐蚀、电化学腐蚀、扫描电镜和透射电镜等测试分析方法,研究了微量Co对7056铝合金组织与腐蚀性能的影响。研究表明,与未添加Co合金相比,添加微量Co的7056铝合金的应力腐蚀寿命提高了22. 57%,应力腐蚀断裂强度从511 MPa增加到559 MPa,应力腐蚀因子从0. 118降到了0. 064。添加微量Co的7056铝合金形成了更加均匀细小的Al3Zr弥散相,更有效地钉扎位错和亚界晶,使基体保持形变回复组织和小角度晶界,抑制再结晶,保持了细小的亚晶组织。亚晶界析出相与晶内接近,从而降低了晶间腐蚀的电化学动力,提升了抗晶间腐蚀性能。此外,其晶界析出相所占面积分数增大,相当于增加了电化学反应过程阳极相对阴极的比例,导致阳极电流减小,晶界析出相溶解速率降低。不连续的晶界析出相能够阻断沿晶界阳极溶解通道,减缓沿晶腐蚀,提高合金抗应力腐蚀性能。

The effect of trace Co element on the microstructures and corrosion properties of 7056 aluminum alloy was studied by metallographic observation,intergranular corrosion test,electrochemical corrosion test,scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results indicated that the 7056 aluminum alloy with trace Co presented a 22.57%increase of stress corrosion life,an improved fracture strength of stress corrosion from 511 MPa to 559 MPa and a dropped stress corrosion factor from 0.118 to 0.064,compared with the alloy without Co.The 7056 aluminum alloy with Co formed more uniform and fine Al3Zr dispersion phase,which effectively pinned the dislocation and subboundary,made the base keep deformation response structure and small angle grain boundary,thus restrained the recrystallization.and kept fine subcrystalline structure.The precipitation phase in the subgrain boundary is close to that in the intracrystalline,which reduced the electrochemical motivation of intergranular corrosion and improved the resistance to intergranular corrosion.Besides,the area fraction of the precipitated phase at the grain boundary increased,corresponding to the increase of the ratio of anode to cathode in electrochemical reaction process,which resulted in a decrease of the anode current and a decrease of the dissolution rate of the precipitated phase at the grain boundary.The disconti-nuous grain boundary precipitates can block anodic dissolution channels along grain boundaries,slow down the intergranular corrosion and improve the stress corrosion resistance of the alloy.