echanical properties of welded Al-Mg Plates differ greatly by the welding methods.The results oftained are summarized as follows:(1) Argon arc method is recomended for Al-Mg alloys, for mechanical propertis welded by this method are the best.(2) Metal arc and oxyacetylene gas method are not recomended for thick Al-Mg plates. Mechanical properties of deposit welded by these methods are extremely inferior to that of mother plates, due to the flux used by those welding methods.(3) Al-Mg thick plates welded by oxyacetylene gas method happen to have hair crack, owing to the welding heat.