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The welding of structural materials, such as aluminum alloys 6063, 6061 and 6005A, does have an adverse influence on the microstructure and mechanical properties at locations immediately adjacent to the weld. The influence of heat input, due to welding and artificial aging, was investigated on aluminum alloy extrusions of 6063, 6061 and 6005A. Uniaxial tensile tests, in conjunction with scanning electron microscopy observations, were done on the: (i) as-provided alloy in the natural temper, (ii) the as-provided alloy artificially aged, (iii) the as-welded alloy in the natural temper, and (iv) the as-welded alloy subject to heat treatment. The welding process used was gas metal arc (GMAW) with spray transfer at approximately 140-220 amps of current at 22-26 volts. The artificial aging used was a precipitation heat treatment for 6 hours at 360oF. The aluminum alloys of the 6XXX series contain magnesium (Mg) and silicone (Si) and are responsive to temperature. Optical microscopy observations revealed the influence of artificial aging to cause change in both size and shape of the second-phase particles present and distributed through the microstructure. The temperature and time of exposure to heat treatment did cause the second-phase particles to both precipitate and migrate through the microstructure resulting in an observable change in strength of the material. Uniaxial tensile tests were conducted for desired specimen thicknesses for sake of comparison. Section 6.4.2-2 of the 2010 Aluminum Design manual discusses provisions for mechanical properties of welded and artificially aged aluminum light poles, fabricated from aluminum alloy 6063 and 6005A. A basis for these provisions was the result of older round-robin testing programs [2, 3]. However, results of the studies were never placed in the open literature. Hence, the focus of this study was to determine the expected mechanical properties of welded and artificially aged 6063, 6061 and 6005A aluminum alloys and publish the results. Tensile tests revealed the welded aluminum alloy to have lower strength, both yield and ultimate tensile strength, when compared to the as-received un-welded counterpart. The impact of post-weld heat treatment on tensile properties and resultant fracture behavior is presented and briefly discussed in light of intrinsic microstructural effects and nature of loading.
The purpose of this report is to summarize the present state of aluminum-welding technology. The major topics covered are: Basic metallurgy of various heat-treatable and non-heat-treatable alloy classes; welding processes used for joining aluminum with emphasis on newer processes and procedures which are considered important in defense metals industries; welding characteristics of various alloys; comparison of tensile properties, cracking tendencies, notch toughness, and stress-corrosion characteristics of various weldments; dissimilar metal welds; and causes of porosity and cracking of aluminum welds and the effect of porosity on weld strength. (Author).
Results of tests show that a slowly rising condenser-discharge preheat current with a rapidly rising welding current afford no less expulsion than a rapidly rising welding current alone, and was inferior to a slowly rising welding current alone. In one case using slowly rising current for preheating and welding proved beneficial although generally, utilizing a raised electrode welding force to decrease expulsion was more practicable. Postheating had no effect on sheart strength until the current sufficient to remelt the welds, which greatly increased the weld diameter and shear strength.
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