INFLUENCE OF MULTI-HOLE TECHNIQUE AND ZINC REINFORCEMENT ON FRICTION STIR WELDING OF DISSIMILAR MATERIALS (AA6061&AISI304)

Abstract

It is tough to get a  quality steels to aluminium alloys joint by fusion welding processes because of the massive distinction between melting temperatures and also the formation of thick brittle Al/Fe intermetallic compounds at the joint interface. In this study, solid-state joining technique was applied to join an aluminium alloy 6061 and AISI 304 stainless steel. The multi-hole technique with a combination of nano sized Zinc filler material and two different pin profiles was used to fabricate the Friction Stir Welding (FSW) joint of  aluminium alloy 6061 and AISI 304L.The amount of zinc filler material, tool geometry and number of passes were varied for better mechanical properties of the joint. A single or double row of holes/grooves was made at the interface of steel to cause initial plastic deformation as well as to add zinc filler material to it. All the joints were fabricated at a constant tool rotational speed of 1120 rpm, tool traverse speed of 20 mm/min  with tool off-set towards steel. FSW joints with zinc filler metal showed improved strength than joints without filler metal. The distribution of the filler material into the base plates  was examined by optical microscope, scanning electron microscope and it was found that uniform dispersion of  filler material took place with an addition of 10 grams of zinc powder and a thin steel-Zn mixing layer structure was revealed at the interface. But the addition of excessive zinc(in case of 20 grams zinc) led to more brittle Interface layers and less adhesive because of  high residual stresses which induces numerous cracks after cooling. It also led to a progressive decrease of the ultimate tensile stress supported by the bond. Therefore the optimum tensile strength was achieved with single row technique ,dual pin tool .Due to critical material mixing and enlarged element diffusion zone the higher micro hardness was observed in a joint fabricated with dual pin ,double row technique and20 grams of zinc.