Study on Wonn Defect in 6061 Aluminum Alloy Friction Stir Welded Plates

Friction stir welding (FSW) is a solid-state joining process where the original
characteristics of metal remain unchanged. The technique results in high joint
strength compared with other welding techniques. It has been widely used fur joining
aluminum alloys in the fields of aerospace, marine, automotive, rail and many other
applications of commercial importance [1]. Some important process parameters that
should be taken into account and control the quality of the weld are the tool spindle
speed (rpm), transverse speed (nun/min), plunging speed (nun/min), dwell time (s)
and depth of penetration (mm). Studies have shown that during FSW, wormhole
(tunnel) defect form along the welded area and the evolved microstructure strongly
affects the mechanical properties of the joint. In this investigation, an attempt has
been made to understand the influence of welding parameters on worm defect in
6061 aluminum alloy plates. For this project, nine (9) different set of welding
parameter combination were used to fubricate the FSW joints. The scope of study is
to butt joined two (2) pieces of 6061 aluminum alloy plates having the dimension of
lOOmm x lOOmm x lOmm and by rigidly clamped both pieces to perform the
welding operation. The project will fucus on tapered pin tool design using AISI H13
Tool Steel Grade. The welding tool will be fubricated using BridgePort PowerPath 15
(CNC Lathe Machine) and undergo heat treatment to increase the hardness level.
Meanwhile, the welding process will be conducted using BridgePort VMC 2216
(CNC Milling Machine). By using Optical Microscope (OM), the size worm defect is
measured. Microhardness measurements were taken on cross sections of the
specimen and were correlated with the size of wormhole defect. The result concludes
that increase in ratio of tool transverse feed rate (S) to tool spindle speed (N) will
result in increase in the wormhole size (mm2) and decrease in Vickers
Microhardness (HV) value.