Abstract
The main aim of this study is to select a suitable tool pin profile to maximize the tensile behavior (Ultimate Tensile Strength and Tensile Elongation) of Friction stir welded aluminum alloys of AA 2024 and AA 6061. The age-hardnable aluminum alloys of 2xxx, 6xxx and 7xxx series are extensively used in automobile and aircraft industries because of its high strength to weight ratio, formability and ductility. These alloys are vulnerable to cracking (2xxx and 7xxx) and highly melt (6xxx) in conventional fusion welding techniques. Friction stir welding is an emerging solid state welding technique which is best suitable for joining these aluminum alloys. The influential process and tool parameters that are affecting the FS welded joints are such as tool rotational speed, welding speed, axial load and tool pin profile. Dissimilar friction stir welded joints of AA 2024 and AA 6061 aluminum alloys are fabricated using a friction stir welding process to examine the influence of the tool pin profiles on tensile properties on various crucial process parameters. A Box-Behnken design with four input parameters, three levels and 30 runs is used to conduct the experiments and Response Surface Method (RSM) is used to develop the mathematical model. The experimental results were predicted at the 95% confidence level. The macro defects in the welds and the modes of tensile fracture are discussed in detail to reveal the root cause of failure in the fabricated samples. The rotating tool equipped with a square pin generated the highest ultimate tensile strength (143 MPa) with a 12% elongation. A microstructure variation on dissimilar alloys which result 44% reduction in tensile strength on AA2024 and 51% reduction in tensile strength on AA6061 aluminum alloys was observed on the stir zones.
Highlights
The conventional fusion welding techniques such as arc, gas welding of age hardnable aluminum alloys (2xxx, 6xxx and 7xxx) are a challenging task for designers and technologists
The difficulties in the fusion welding process are associated mainly related to the presence of the oxide layer, solidification shrinkage, high coefficient of thermal expansion, high thermal conductivity and other gases in a molten state (Shanmuga Sundaram and Murugan, 2010)
The mathematical models were developed at 95%
Summary
The conventional fusion welding techniques such as arc, gas welding of age hardnable aluminum alloys (2xxx, 6xxx and 7xxx) are a challenging task for designers and technologists. The difficulties in the fusion welding process are associated mainly related to the presence of the oxide layer, solidification shrinkage, high coefficient of thermal expansion, high thermal conductivity and other gases in a molten state (Shanmuga Sundaram and Murugan, 2010). Joining these alloys using fusion welding techniques leads to the melting and re-solidification of the fusion zone, results the formation of brittle inter-dendritic structure and eutectic phases. The formation of brittle structure in the weld zone results a drastic loss of mechanical properties (Rhodes et al, 1997; Su et al, 2003).
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