Welding of 6061-T651 Aluminium and the relationship of tensile properties to hardness in the heat affect zone. ENG919 Dissertation

Two objectives are envisaged for this work; the first is to conduct a literature review of 6061 aluminium and welding practices for this alloy and current best welding practice with an emphasis on welding for nuclear applications. Recent developments in the use of innovative welding practice will also be reviewed. The intention is to provide a background of information in order to avoid weld-related problems that have the potential to shorten the life of expensive and difficult-to-replace critical components. The literature survey will include a review of the base alloy and the effect of welding on the mechanical properties in the weld zone (weld metal and heat affected zone (HAZ)). Included, as part of this objective is to review the welding of aluminium to create an awareness of potential difficulties for future critical welding applications. The literature survey would also include the aspect of nuclear-induced changes in properties, particularly within the weld zone. This element of the survey would investigate factors for consideration in selecting the welding method and filler material. The American Society of Mechanical Engineers (ASME) have a nuclear Code Case (N519)14 covering the use of 6061 aluminium in nuclear core components. This Code Case calls for the implementation of a surveillance program to monitor changes in properties during service. The literature survey will address this requirement and make a set of recommendations as a first step towards implementing such a program. A second objective is to develop a model that relates mechanical properties to hardness measurements in the weld zone. This model has the potential to be used as a tool for checking weld metal properties and the extent of changes in HAZ properties. The intention is to thermally overage the base alloy to various hardness values and relate the hardness to tensile and Charpy impact toughness values. Welded test plates will be prepared using Gas Metal Arc Welding (GMAW) and Tungsten Metal Arc Welding (GTAW) with a 4043 filler material. Thermocouples will be embedded within the weld test plates to gain a measure of heating and cooling rates and maximum temperature attained at various distances from the weld. Miniature test samples will be extracted from various zones of the HAZ parallel to the weld line. These samples will be tested to relate hardness to tensile properties. Comparisons will be made between the welded sample results and the results induced by an over-aging heat treatment of the base alloy to determine if heating rate is important (author)