1977 Volume 46 Issue 3 Pages 146-151
The authors studied on the effect of addition to shielding argon of some polyatomic gases upon the geometry of MIG spot weldments of aluminum alloys and upon the prevention of weld cracking. Furthermore they studied on the possibility of improving the tensile properties of spot welded joints by using pressurized shielding gas mixture consisting from argon and a small amount of carbon dioxide. The conclusions are summarized as follows:
(1) Addition to shielding argon of so small an amount of 1 to 5% carbon dioxide or oxygen alters ;he fusion zone contour from finger- to bell-type. Furthermore it increases the depth of penetration and the diameter of fused zone in the interface, and decreases the outer diameter of spot weldment.
(2) Corresponding to the above alteration of weld geometry cracking is effectively prevented.
(3) With increase in additive quantity of carbon dioxide or oxygen the surface of spot weldment becomes rather dirty. But from the standpoint of practical usability it may be permissible to add up to 3% carbon dioxide to argon.
(4) To investigate the effects of addition of polyatomic gases to shielding argon on the mechanical properties of weld metal, tensile tests are performed of butt welded joints made by using carbon dioxide or oxygen added argon gas shielding. The results show that up to 5% addition of carbon dioxide or oxygen has no detrimental effect upon the tensile strength of weld metals.
(5) Spot welding at higher ambient pressure together with shielding gas mixture consisting from argon and a small quantity of carbon dioxide gives most preferable fusion zone contour.
(6) Spot welding with 2.4% carbon dioxide added argon gas shielding at 3 atm ambient pressure makes it possible that variation of tension shear strength of a series of spot welded joints can be met the JIS requirement imposed on resistance spot welds that the variation should be smaller than 25%.