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%.
In order to get higher strength and toughness of steel weld metal, effects of microalloying elements on the strength and toughness of 0.01%C cast steel specimens in stead of steel weld metal have been investigated. The microalloying elemtns used were Al, Ti, Zr, Nb and V. The findings of the experiment are as follows; 1. Aluminum addition up to 0.076% decreases the transition temperature of as-cast specimen, but does not increase the strength. 2. Niobium addition of 0.02% increases the strength without sever reduction of toughness. 3. Titanium, zirconium or vanadium additions increase the strength of as-cast specimens, but reduce the toughness severly.
5083 aluminum alloy plate of 50 mm thickness was welded by high current MIG process. Then, Charpy impcat test was performed on base and weld metal at both room temperature and -196°C. In Charpy test, load-time curves were photographed and crack initiation energy and crack propagation energy were obtained from these curves. Charpy impact values in the weld metal had lower values at -196°C than at room temperature and each value tended to decrease at both temperatures when a value of a parametery increased. The values ofy=0 and 100% represent the fusion boundary and center of the weld metal, respectively. Both crack initiation energy and crack propagation energy decreased also when the parametery increased. Mg content dissolved in the weld metal which had been obtained by X-ray diffraction technique decreased when the parameter y increased. At the center of the weld metal the dissolved Mg content near the specimen surface was less than near the root of the weld metal. The change of the dissolved Mg content affected the crack initiation energy. That is, the crack initiation energy increased approximately linearly when the dissolved Mg content increased. Fractographs fractured at room temperature showed dimple patterns. On the contrary, quasi-cleav-age like structure was mainly observed on the fracture surface tested at -196°C and many sub-cracks were also observed.
The effect of slag basicity on silicon and manganese deoxidation in the submerged-arc welding process is considered by bead-on-plate welding performed using agglomerated fluxes of CaO-MgO-Al2O3-SiO2 system. Dissolved oxygen content in molten pool is remarkably affected by oxygen which is originated from dissociation of silica in slag, then oxygen content in weld metal can be decreased by a reduction of the activity of silica. The arc cavity is almost filled with CO gas, and PCO2/PCO in the atmosphere is decreased with increasing slag basicity. Ratio of oxygen content in weld metal to FeO content in slag takes a constant value independently of the slag basicity. Oxygen in weld metal deposited with MnO-free fluxes seems to be quasi-equilibrium relation with silicon at about 1950°C independently of manganese content in weld metal.