Kamaraj M

Electron beam welds of aluminum alloy 2219 offer much higher strength compared to gas tungsten arc welds of the same alloy and the reasons for this have not been fully explored. In this study both types of welds were made and mechanical properties were evaluated by tensile testing and pitting corrosion resistance by potentio dynamic polarization tests. It is shown that electron beam welds exhibit superior mechanical and corrosion properties. The weld metals have been characterized by scanning electron microscopy; transmission electron microscopy and electron probe micro analysis. Presence of partially disintegrated precipitates in the weld metal, finer micro porosity and uniform distribution of copper in the matrix were found to be the reasons for superior properties of electron beam welds apart from the fine equiaxed grain structure. Transmission electron micrographs of the heat affected zones revealed the precipitate disintegration and over aging in gas tungsten arc welds. © 2005 Published by Elsevier Inc.

The present work pertains to the improvement of high temperature stability of age hardenable AA2219 aluminium-copper (6.3%) alloy. Addition of scandium, magnesium and zirconium to the base metal AA2219 was adopted to improve this high temperature stability. These additions were systematically varied by preparing alloys of different composition using gas tungsten arc melting. Long time ageing studies and impression creep technique were used to study the high temperature stability of the alloys. These modified compositions of the alloy resulted in fine equiaxed grains, refined eutectics, large number of high temperature stable and finer precipitates. Among all the compositions, 0.8% Sc + 0.45% Mg + 0.2% Zr addition was found to be significant in improving the high temperature stability of AA2219 alloy. This may be attributed to the possible microstructural changes, solute enrichment of the matrix and pinning of the grain boundaries by the finer precipitates. © 2007.

Weld metals of AA 2219 (Al-6%Cu), welded with 2319 filler, exhibit yield strength values of about 40% compared to their base metal counterparts. This study is an attempt to improve the yield strength of 2219 welds by using fillers containing scandium. Pitting corrosion behavior of the welds has also been studied. Welds were made with Al-Cu, Al-Cu-Sc, Al-Mg, and Al-Mg-Sc fillers. Manual AC-TIG process has been employed to weld 8.5mm thick 2219 -T87 alloy plates. Tensile and corrosion behavior of welds was studied and results were substantiated by metallography. Metallographic studies showed extensive grain refinement in welds made of scandium containing fillers. Presence of scandium, improved the resistance to cracking in case of welds made of Al-Mg fillers. Improvement in mechanical properties has been observed due to the presence of scandium and the rise in percent elongation was significant. Crack free welds with significant improvement in mechanical properties were obtained with a weld metal composition having small amounts of Mg and Sc. Scandium addition did not alter the pitting corrosion resistance of the weld metals. Magnesium containing weld metals were found to be inferior in terms of pitting corrosion resistance.

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0.16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0.37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM-EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equlaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure. © 2005 Institute of Materials, Minerals and Mining.