Papers by Author: S.R.S. Bakar

Abstract: This paper presents an investigation on microstructure and mechanical properties of welded AA 6061-T6 plate using filler metal ER 4043 in the Gas Metal Arc Welding (GMAW) process. Double pass welding technique on both sides of 5 mm thick plate or more is required to provide sufficient weld pool in the joint. The weld metal of the first welding pass exhibits finer microstructure than the second welding pass. The size of Mg₂Si precipitations in the heat-affected zone (HAZ) region is larger than in the base metal due to the welding process that reheats the alloy from the T6 condition above the eutectic temperature. Rapid cooling of the first pass and moderate cooling rate for the second pass during weld metal solidification eventually resulted in significantly change the shape and size in the microstructure that had affected the hardness and mechanical properties. Comparisons made to the base metal on the hardness test results found that the hardness of first pass weld metal dropped by 15%, and by 37.5% for the second weld metal, while the hardness at the boundaries of the first and second weld metals dropped by 32.5%. The ultimate tensile strength and strain of the weld joint with ER 4043 also decreased by 48% and 94% respectively. Based on the findings of the study, it is concluded that even though the double sided welding technique is able to overcome shallow weld penetration to avoid stress concentration that leads to the fatigue failure, the metallurgical changes eventually contributes to degradation of mechanical properties.

Abstract: Effect of porosity distribution in the weld metal of AA 6061-T6 with 6 mm thickness plate using two dissimilar filler metals in the gas metal arc welding (GMAW) process was investigated. This paper provides a characterization of the porosity in term of the distribution, location and size of the pores in the weldment region. The porosity characterization was made by using 3D X-Ray Computed Tomography and Scanning Electron microscope. The existing pores resulting from the cause of the filler metal in welded alloy used ER4043 (Al-5Si) was compared with the weldement used ER5356 (Al-5Mg). From this investigation, it is exhibited that the pores only distributed and located mainly at the edges and at the root of the weldment with ER5356 weld metal, however, for weldment with ER4043, the pores were mainly scattered in the centre region. The distribution and location of pores in weld metal is believed due to the effect of convections in the molten metal, solidification rate and also from the gases induced during the weld process. Apart from that, results of tensile test indicated the weldment has affected the strength and ductility of the two different fillers selected. AA6061 with ER5356 are dropped 50% in ultimate tensile strength (UTS) and 40 % in elongation; meanwhile AA6061 with ER 4043 was dropped 70% in UTS and 90% in elongation. The different principle alloying element of these two filler metals have play significant role in the distribution of porosity in AA6061 weldment and had influence the strength and ductility of the weld joint.

Abstract: The purpose of this study is to evaluate the effect of filler metals in the gas metal arc welding (GMAW) process on the Aluminium alloy of AA 6061-T6 welded joints. 6 mm thickness plate with single V butt configuration was used and welded using two different fillers ER 4043 and ER 5356 and controlled welding parameters. The relationship between hardness and microstructure of the welded parts were studied and compared and the results showed that the post weld mechanical property has decreased especially for the filler ER 5356. The hardness at the heat affected zone (HAZ) of ER 5356 also has reduced almost 85% compared to the hardness of AA 6061 base metal. The microstructure of ER 4043 welding material shows the shape of columnar grains and dendrite structure. Microstructure morphology of ER 5356 welding material shows dendrites and intermetallic particles (Mg2Si) have partially dissolved and scattered in the welding material.