Abstract: The SCC experiments on welded joints of high strength aluminium alloy LY12CZ indicate that both Active Path Corrosion and Hydrogen Embrittlement Cracking of the LY12CZ welded jonts can occure with the change of the polarization potentials.However,it is Active Path Corrosion under no extrapolarizations.The SCC model is established that the SCC of the LY12 CZ welded joints initiates and propagates along the precipitation free zone in the overaged zone of the weldes joints according 1o the theoretical analysis and the experimental results.