Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. However, the fundamental knowledge of the friction stir welding process in relation to steel remains relatively limited. A microstructure and property evaluation of friction stir welded low alloy steel grade DH36 plate, commonly used in ship and marine applications has been undertaken. In this comprehensive study, plates of 2000 x 200 x 6 mm were butt welded together at varying rotational and traverse speeds. Samples were examined microscopically and by transverse tensile tests. In addition, the work was complemented by Charpy impact testing and micro-hardness testing in various regions of the weld. The study examined a wide range of process parameters; from this, a preliminary process parameter envelope has been developed and initial process parameter sets established that produce commercially attractive excellent quality welds through a substantial increase in the conventionally recognised weld traverse speed.

A series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW). Comparator welds in the same thickness from the same plates were produced using a single sided single pass process submerged arc welds (SAW). This work was carried out to evaluate the mechanical properties of FSW material with a view to its possible application in a shipbuilding production process route. Overall, the performance of the FSW material was superior to the SAW comparators. Areas such as distortion and fatigue were particularly positive in the FSW material. An 8 mm thick plate was also produced using two FSW passes, one from either side, and it was found to have superior toughness and fatigue performance when compared to the single sided 8 mm FSW material. Some of these benefits are thought to have originated from the internal overlap zone between the two passes.

No abstract

A new method of supplying shielding gases in an alternating manner has been developed to enhance the efficiency of conventional Gas Metal Arc Welding (GMAW). However, the available literature on this advanced joining process is very sparse and no cost evaluation has been reported to date. In simple terms, the new method involves discretely supplying two different shielding gases to the weld pool at pre-determined frequencies which creates a dynamic action within the liquid pool. In order to assess the potential benefits of this new method from a technical and cost perspective, a comparison has been drawn between the standard shielding gas composition of Ar/20%CO2, which is commonly used in UK and European shipbuilding industries for carbon steels, and a range of four different frequencies alternating between Ar/20%CO2 and helium. The beneficial effects of supplying the weld shielding gases in an alternating manner were found to provide attractive benefits for the manufacturing community. For example, the present study showed that compared with conventional GMAW, a 17% reduction in total welding cost was achieved in the case of the alternating gas method and savings associated with a reduction in the extent of post weld straightening following plate distortion were also identified. Also, the mechanical properties of the alternating case highlighted some marginal improvements in strength and Charpy impact toughness which were attributed to a more refined weld microstructure

Studies have been carried out to determine the effects of implementing alternating shielding gases for 6082T6 aluminium alloy welding. Alternating shielding gases is a newly developed method of supplying shielding gases to the weld area to enhance the efficiency of the standard gas metal arc welding process.Alternating shielding gases involves discretely supplying two different shielding gases to the weld zone at a predetermined frequency that creates a dynamic action in the weld pool. Several benefits have been identified in relation to supplying shielding gases in this manner, including reduced porosity, marginal improvements in mechanical properties, increased travel speed, and as a result of the lower heat input, reduced distortion. This method of shielding gas delivery therefore presents attractive benefits to the manufacturing community; namely the increased productivity and quality, in addition to a reduction in the amount of post-weld straightening required.However, the literature available on this advanced joining process is very limited, especially so for aluminium alloys. For this reason, an evaluation has been carried out on the application of alternating shielding gases for the gas metal arc welding process on 6082T6 aluminium alloys.

No abstract

This study investigated the properties and microstructures of EH46 microalloyed steel following double-sided friction stir welding. The partially welded material was reversed, completing the weld. Yield strength, elongation and toughness of the weld were similar to those of the base material. During welding, the ferrite-pearlite in the base material transformed to mainly upper bainite, but the overlap or interference zone in the centre of the weld consisted predominantly of 0.5-3 µm recrystallised ferrite grains. The microhardness increased from 240 HV in the base material to 350 HV in bainite but decreased 200-240 HV in the overlap zone. These substantially differing microstructures suggest that the overlap or interference zone was processed at a lower temperature than the remainder of the weld, probably in ferrite.

A new method of supplying shielding gases in an alternating manner has been developed to enhance the efficiency of conventional gas metal arc welding (GMAW). However, the available literature on this advanced joining process is very sparse and no cost evaluation has been reported to date. In simple terms, the new method involves discretely supplying two different shielding gases to the weld pool at predetermined frequencies which creates a dynamic action within the liquid pool. In order to assess the potential benefits of this new method from a technical and cost perspective, a comparison has been drawn between the standard shielding gas composition of Ar/20%CO2, which is commonly used in UK and European shipbuilding industries for carbon steels, and a range of four different frequencies alternating between Ar/20%CO2 and helium. The beneficial effects of supplying the weld shielding gases in an alternating manner were found to provide attractive benefits for the manufacturing community. For example, the present study showed that compared with conventional GMAW, a 17 per cent reduction in total welding cost was achieved in the case of the alternating gas method and savings associated with a reduction in the extent of post-weld straightening following plate distortion were also identified. Also, the mechanical properties of the alternating case highlighted some marginal improvements in strength and Charpy impact toughness which were attributed to a more refined weld microstructure