Corrosion Resistance Of Friction Stir Welding LY12Aluminum Alloy

In this paper, immersion corrosion tests and electrochemical tests have been donefor friction stir welded LY12(CZ) aluminum alloy. Microstructure and corrosionmorphology were observed using OM and SEM. The polarization curve of every areain joints was tested by electrochemical workstation.The influence of welding processparameters on corrosion resistance in3.5%NaCl solution and the sensitivity of inter-granular corrosion was researched. The mechanism of different regionns in the jointswas discussed.The results indicates that the corrosion potential in weld center shift negatively,current density increased and resistance corrosion gradually reduced in3.5%NaClsolution from top to bottom. However, the trend in HAZ and TMAZ is inversed, andthe corrosion resistance of HAZ and TMAZ on the advancing side was lower than itson retreating side. As welding speed and rotating speed of the tool increasing, thecorrosion resistance in TMAZ，SDZ and the NZ increased, the corrosion resistance inHAZ did not change. The corrosion resistance of joints was most serious when therotary speed of475r/mm and welding speed of30mm/min.Corrosion resistance ofdifferent regions in the joint was impacted primarily by the microstructure.The sizeof the second phases in weld center increased, and precipitated intensively in the NGfrom top to bottle.The electrochemical inhomogeneity increased，and the corrosiondegree increased.Because the size of the second phases in HAZ and TMAZ was thelargest, and the electrochemical homogeneity decreased, the corrosion resistance wasthe worst in the joint.The results of intergranular corrosion test showed that it was insensitive tointergranular corrosion in the HAZ, TMAZ and SDZ.The parent material occurredslightly intergranular corrosion. However, the sensitivity of intergranular corrosion inthe NG was highest in the joints, and increased with welding speed increasing andchanged little with constant rotating speed of the tool.The sensitivity of intergranularcorrosion was significantly effected by the welding line energy.When the value of n/vwas5r/mm, the sensitivity in the NG was intense. When the value of n/v was15.8r/mm, the sensitivity was slight.As the value of n/v increasing, the sensitivity decr-eased gradually, and remained at relatively low level. The results of stress corrosion tests showed that there was insignificantly affectedon the corrosion of the joint by low stress. Due to shear stress, there was about45°"corrosion Groove" with the direction of load in joint at320MPa. HAZ and TMAZoccurred Overaged softening for welding thermal cycle, and microstructure fluc-tuation increased. The Degree of “corrosion Groove” increased. However the NG hadhigher strength, and the microstructure was homogenous. The Degree of “corrosionGroove” was small.