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An investigation has been carried out of the effects of tool probe shape and size on the formation of surface composite by uniformly distributing SiC particles into a surface layer of an A1050-H24 aluminium plate through friction stir processing (FSP). Tool probes of three different diameters (3, 5 and 7 mm) and four different shapes (circular with threads, circular without threads, square and triangular) have been used to fabricate the surface layers at rotation speeds of 1500–2250 rev min–1 and a travelling speed of 1·66 mm s–1. The SiC particles were packed into a groove of 3 mm width and 1·5 mm depth cut on the aluminium plate and covered by an aluminium sheet of 2 mm thickness. A rotating tool was plunged into the plate through the cover sheet so that the tip of the probe reached beyond the bottom of the groove. As a result, it was found that the square probe dispersed the SiC particles homogeneously in the nugget zone compared with other probe shapes regardless of the rotation speeds. Furthermore, the distributed particles and also the aluminium matrix grain size became finer by the use of square probe than those of the other shapes. On the other hand, the wear rates of the square and triangular probes were higher than that of circular shape. The worn iron debris from the tool reacted with aluminium matrix and form fine iron aluminides compound dispersed in the nugget zone. The probe size had limited effects on the homogeneity of the SiC particles distribution in the nugget zone; the distribution of SiC particles obtained by triple FSP passes was less homogeneous when the probe size was smaller. Microhardness of the nugget zone was homogeneously increased to a level as high as 60 HV with tool of square probe shape after three passes to be compared with 23 HV of the aluminium matrix beside the nugget zone. [ABSTRACT FROM AUTHOR]

A feasibility investigation has been carried out of the formation of surface composite by uniformly distributing SiC particles 125 µm in size into a surface layer of an A 1050-H24 Al plate through friction stir processing (FSP). The SiC particle was filled into a groove cut on the Al plate, covered by an Al sheet 2 mm thick, and a rotating tool was penetrated from the cover sheet so that the probe tip reached a depth beyond the groove bottom. The effects of process parameters (rotation speed and travelling speed) and applying multiple passes on the distribution of SiC particle in the nugget zone were investigated. The effects of groove size and its position relative to the tool probe were also investigated. Applying multiple passes had a great effect on the homogeneity of the SiC particle distribution. At rotation speeds of 2000–3000 rev min-1, the SiC particles tended to cluster in some places in the nugget zone. By decreasing the rotation speed to 1000–1500 rev min-1, the SiC particle was distributed in almost all the nugget zone area when the groove was 2–3 mm wide and 15 mm deep. On the other hand, the stirring action of FSP was insufficient to distribute homogenously the SiC particles when the groove size was increased to 3×2 mm. By shifting the groove position towards the advancing side of the tool probe, the distribution of the SiC particles in the nugget zone became better. The defect free nugget zone with homogenously distributed SiC particles was obtained in a sample produced by FSP at rotation speeds of 1500 rev min-1 for the first pass and 1250 rev min-1 for the second and third passes. Microhardness of the nugget zone was increased to a level as high as 55 HV when the groove size was 3×15 mm. The effect of the rotation speed on the particles dispersion was discussed with particular reference to the vertical material flow in the nugget zone. [ABSTRACT FROM AUTHOR]

The effects of shielding gas composition on the properties and microstructure of single pass weld metals produced by GMA (gas metal arc) groove welding of 950 MPa class steel plates have been investigated. The shielding gas employed was a mixture of argon (Ar) and carbon dioxide (CO2) (0–25%), and the weld heat input was ∼3 kJ mm. With increasing CO2 content, the hardness of the weld metal decreased from 380 HV to 280 HV, and the absorbed energy of the Charpy impact test decreased from 130 J to 90 J. The microstructures of the weld metal, consisting primarily of low carbon martensite and carbide free bainite, became more bainitic as the CO2 content of the shielding gas was increased. It was also found that the MA constituent, embrittling microstructure, was formed in the granular bainitic area, the volume fraction of which increased with the CO2 content of the shielding gas. [ABSTRACT FROM AUTHOR]

A shielding gas composition-controlled (SGC) welding process has been developed in which shielding gas composition changes periodically. This welding process has been successfully developed on the basis of computer simulation. A simulation model incorporating periodic change of shielding gas composition has been proposed and verified by welding experiments and observation of wire tip behaviour. In order to change shielding gas composition effectively, CO2 gas is locally and periodically introduced into Ar + 2%O2 shielding gas. As a result, CO2 and MIG arcs occur periodically during welding and the arc pole strongly oscillates over the groove wall. Oscillation control of the arc pole can be achieved by this shielding gas composition-controlled method. This newly developed welding system makes it possible to perform stable welding in narrow V-grooves and excellent welding joints are obtained with good fusion. [ABSTRACT FROM AUTHOR]