Effect of Surface Treatment in High Vacuum on Solid Phase Weldability

Abstract

The purposes of this study are to explain the effect of surface cleanliness on the solid phase weldability of metals, and to clarify the influences of welding factors such as temperature, pressure and duration on the mechanical strength of the welded joint In the experiment, the surfaces to be welded are polished by a wire brush made of stainless steel in the environment in the ranges 760-2×10^-6 torr and then these metals are welded without melting under various welding conditions. The quality of the welded joint is evaluated by the tensile shear test at room temperature and the following results are obtained.
1. The wire-brushing in high vacuum is a very useful technique for the improvement of the weld quality, and that the surface cleanliness of metals to be welded is a principal factor for the solid phase welding in high vacuum.
2. The quality of welded joint is affected by the surface treatment and welding atmospheric pressure or the exposure to the environment befor welding, and these influences become more and more remarkable with a decreasing welding temperature.
3. The effects of the welding temperature and pressure on the mechanical strength of the solid phase weld made in high vacuum are noticeably greater than those of the welding duration.
4. In the solid phase welding at the temperature of the order of 35 percent of the absolute melting temperature of metal to be welded, the weldability of the metal is mainly affected by the reaction between the metal to be welded and the residual gases in vacuum chamber. Therefore, the solid phase weldability of the metal such as silver and copper which has much weaker affinity for gaseous oxygen is better than that of the metal such as magnesium, aluminum and titanium which has much stronger affinity for gaseous oxygen.