Osamu Ohashi

Behavior of oxide film on intimate contact zone of diffusion-weld - Study on surface film on diffusion-welded interface (Report 3)

Behavior of the oxide film on the intimate contact zone of diffusion-welded interface has been investigated with Auger electron spectroscopy, SEM and EPMA. Results obtained are summarized as follows.1. Behavior of the oxide film on the intimate contact zone of iron, SUS304 stainless steel, copper and titanium is similar to that on the void surface of diffusion-welded interface.2. On the diffusion-welded interface of aluminum, the oxide film is disrupted to form metallic bonds by the deformation of contacting asperities. As the oxide film of aluminum does not disappear during welding, tensile strength of welded joint is low.3. On the intimate contact zone of diffusion-welded joints in copper, iron and SUS304 stainless steel, inclusions are formed owing to spheroidizing of the oxide film. Inclusions consist of various oxides and sulfides. The amount of inclusions decreases with a decrease in the thickness of the oxide film of welded surface and with a increase of welding time.4. Behavior of the oxide film on diffusion-welded interface can be classified to three types as follows:A type-The oxide film on void surface and intimate contact zone disappears during the initial stage of diffusion welding. Titanium belongs to this type.B type-The oxide film on void surface and intimate contact zone disappears, forming inclusions owing to spheroidizing of the oxide film. The amount of inclusions decreases owing to diffusion of oxygen during welding. Copper, iron and SUS304 stainless steel belong to this type.C type-The oxide film on diffusion-welded interface does not disappear during welding. Aluminum belongs to this type.

Effect of welding atmosphere on mechanical properties of diffusion-welded joint.

Diffusion-welded joints were made under welding atmosphere such as vacuum at 4 and 4×10-3 Pa, and Ar, H2 and air at 1×105 Pa. Better welding atmosphere for diffusion welding was investigated from the estimation of mechanical properties of diffusion-welded joints, defects such as void and inclusion, and residual gas in voids of diffusion-welded joints. The materials used were SUS304 stainless steel and Ti-6Al-4V alloy, and the results obtained are as follows:1) The best welding atmosphere is vacuum at 4×10-3 Pa for both materials in five kinds of welding atmosphere used.2) For the good selection of welding atmosphere, it is necessary to consider three items as follows.a) Welding atmosphere which does not have influence on quality of base metal.b) Welding atmosphere which does not oxidize the welding surface.c) Welding atmosphere which does not remain in voids.3) At diffusion-welded joints made under Ar atmosphere, Ar remains in voids of diffusion-welded joints. Ar does not diffuse into the base metal at all, and prevents the shrinkage of voids.

Local flashing phenomena of metal sheets. Study on flash welding: Part 4.

In previous studies, the total flashing phenomena of the specimen to be welded have been discussed from the waveforms of flashing voltage and flashing current of the steel sheets.The purpose of this study is to examine the flashing phenomena of limited part of the specimen to be welded. The materials used are of carbon steels, copper and aluminum sheets. The local flashing phenomena of the specimen to be welded are detected by the intensity of the light from the part through the slit of 1.2 mm width placed in 7 mm from the welds. The following results are obtained.1. The local flashing is a discontinuous phenomenon, namely the flashing of several times occur at intervals of 1 or 2 ms after the flashing off of 10 up to 40 ms or 40 ms and over.2. Such a periodical flashing is extensively in evidence during the flashing of low or medium carbon steel, copper and aluminum.3. There is a secondary no load voltage that makes the maximum number of local flash times. The voltage is of about 6 volt in this experiment of low carbon steel sheet.4. The mechanical properties of the welded joint of low carbon steel sheet can not attain to the excellent results under the conditions of the secondary no load voltage that makes the maximum number of local flash times.5. There is risk of upsetting the several parts of the specimen after the flashing off of more than 10 ms, even if the carbon steel sheets are welded under the optimum welding conditions.