o Taka

Spot welding of aluminium and steel sheet with an insert of aluminium clad steel sheet: Dissimilar metal joining of aluminium and steel sheet (1st Report)

Summary This paper describes an investigation of the dissimilar metal spot welding of aluminium and steel sheet with an aluminium clad steel sheet insert. The study relates to application of this system in automotive fabrication in an effort to reduce motor vehicle weight. To ascertain the mechanical properties of the intermetallic compounds formed at the steel and aluminium bond interface, measurements were performed using four types of Fe‐Al binary system intermetallic compound. The mechanical properties of spot‐welded joints in aluminium and steel sheet with and without insertion of an aluminium clad steel sheet were measured by the cross tension test, and the microstructures of the welded joints then formed were observed. The intermetallic compounds FeAl and Fe3Al have a relatively high ductility, and Fe2Al5 and FeAl3 have a high hardness and low ductility. Fe2Al5 intermetallic compounds were formed in the spot‐welded zones of the aluminium and steel sheet, resulting in loss of strength. The dissimila...

SOFTENING IN WELD HEAT AFFECTED ZONE OF DUAL PHASE STEEL SHEET FOR AUTOMOTIVE WHEEL RIM

Dual phase steel offers potential for wheel weight reduction, but has not been completely succeeded, in part, because of a localized necking or a fracture during rim fabrication. This failure should be related to a softening in the weld heat affected zone (HAZ). This paper investigates mechanical properties through microstructural change produced in the HAZ of as-rolled dual phase steel and finally suggests a practical solution. The softening, caused by heating the steel up to Ac1 in the HAZ, is found to be affected not only by tempering of martensite, but also by the variation of hardness in ferrite matrix. Moreover strain aging as well as work hardening due to up-setting stage during the flash welding also concerns this problem. Coiling temperature in manufacturing as-rolled dual phase steel has a large effect on the conditions of ferrite and martensite. Control of the temperature is of great importance to avoid such a localized necking or a fracture in the HAZ.

Effect of Chemical Compositions on Properties of Root Bead Surface in TIG Arc Welding. Effect of Chemical Compositions on Weldability in Fabrication in High Alloyed Steel. Report IV.

The effects of chromium and silicon contents on the roughness of root bead surface in gas tungsten inert gas arc welding without inert gas backing was investigated from a point of view of the oxide layer formed on root bead surface. Test welding was carried out on plates containing various contents of chromium and silicon. The roughness of root bead surface was measured by observation of a cross section of weld metal. The thickness of the oxide layer was also measured and chemical compositions were analyzed by EPMA. The roughness of root bead surface increased in weld metals with higher chromium content as a result of the random formation of thick and porous oxide on the root bead surface. The increase of silicon content improved the roughness of root bead surface. The thickness of oxide on root bead surface was thinned by increasing the silicon content and the high silicon concentration was detected at the interface of oxide and the weld metal. From these results, the improvement of roughness of root bead surface by silicon was considered to be due by preventing the random growth of oxide by the formation of a dense silicon oxide layer as a barrier of oxygen diffusion at the interface of oxide and weld metal. The increase of roughness by increasing the chromium content was also considered to be caused by the formation of thick and porous oxide as a result of the prevention of the formation of uniform and dense oxide layer of silicon.