純金屬與鋁合金結合之殘留應力對腐蝕的影響

The Effect of Residual Stress on the Corrosion Behavior in Pure Metal/Al Alloy Joints

本研究在探討以焊接為例，因製程所引起之局部異質性（Heterogeneity）或殘留應力（Residual Stress）在海洋應用環境中之腐蝕行為。一系列摩擦焊接之同金屬接合的碳鋼／碳鋼、不銹鋼／不銹鋼，與異金屬相接合的碳鋼／不銹鋼、純銅／5086鋁合金、純鋼／7075鋁合金之固態結合，用來探討接合區附近異質性存在對構件機械質、化學腐蝕行為之影響。一般所言摩擦焊有較佳之機械性質，極為籠統。經此研究結果，可較為具體指出摩擦焊接合棒，以鋼鐵為例，其接合區具有極佳抗扭力，斷裂位置均發生在素材，而非接合線上（Bond Line）。抗拉力言摩擦焊件較素材有較高的降伏強度及最大合的拉力斷裂位置卻發生在接合線上。摩擦焊件結合線附近硬度分佈呈現非均匀之分佈，與其焊接所使用壓力、材料熱傳導係數、材料之熱處理性等因素有關，導致內外徑硬度高低不一致，熱影響區大小及幾何形狀亦不同。電弧自體接合的板狀純銅與鋁合金7075、5086、5356和2024接合，經Ray測量結果顯示，在對接焊道附近有拉伸殘留應力存在。依據鋁合金端殘留應力測試趨勢，擇點做海水腐蝕測試，其結果顯示7075鋁合金之殘留拉應力焊道區，要比殘留壓縮應力存在的母材中間區為活性，故腐蝕會發生在成為陽極的焊道及其附近。反之，鋁合金5086、2024因正負殘留應力大小差距不大，則無非常明顯的腐蝕行為差異。

Friction welding and TIG welding of dissimilar metals were chosen as the examples to study the effect of local heterogeneity and residual stress induced by manufacturing process on the corrosion behavior inlication. A series of solid-state bonding of similar metals and dissimilar metals by friction welding were utilized to investigate the influence of heterogeneity in the heat affected zone on the local mechanical properties and local electrical chemical crosion behavior. This study points out the bond region of friction welding has an excellent torsion resistance than the base metals. Torsion fracture always occurs at the base metals rather at the bond line region. The similar and dissimilar metal join of friction welding have the higher yield strength and ultimate tensile strength than the single base metal due to the metallurgical notch strengthening effect. However, in some cases of friction joints, the tensile fracture occurs at the bond line instd of base metal. Microhardness of the friction welding demonstrates a non-unform distribution. Geometrical shape and size of the heat affected zone varies with the factors of external pressure, heat conductivity of the materials and heat-treatability ofhe materials etc. The pure copper plate was butt jointed with the aluminium alloy plate of 7075, 5086, 5356 and 2024 by autogeneous welding process of TIG. The results of surface residual stresses show that high tensile stress exists at the weld and thedjacent region of the weld. The results of corrosion illustrate that the high tensile stress area is more electro-chemically active than the compressive stress area. Thus corrosion preferrs to happen at the anodic weld and the adjacent.