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Title: Study of mechanical properties and weld metal porosity on mechanised MIG aluminium alloy 5083 weldments
Author: Winarto
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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Several AA-5083 welds were fabricated using the mechanical MIG welding process with different welding parameters and two different filler wires. The investigation focuses on the effect of welding variables such as current, welding speed, and heat input (linear energy) on mechanical properties and weld metal porosity in AA 5083 weldments. Image analyses was used to determine the percentage of weld porosity. Results shows that the weld porosity observed in all welds varies with welding parameters employed. The percentage of porosity decreases with increasing welding current range from 250 to 280 A, as it does as the welding speed increases from 8.33 to 11.24 mm/s. However, porosity increased with increasing heat input from 596 to 703 J/mm. Moreover, the percentage of porosity in welds with the ER5087 filler wire was considerably lower than that of welds with the ER55565A filler wire. All weldments had the UTS, the yield strength and elongation in the range of weld mechanical properties standard according to EN and ASTM Standard. The porosity appeared to have a much reduced effect on the strength of weldments. Analysis of the hardness profiles across the weld interface was employed for both welds using ER5556A and ER 5087 filler wire. The hardness values vary with welding parameters employed. The trend shows that increasing arc power input (Q=EI) by increasing welding current, produces increased erratic hardness distribution. Some welds with a high arc power input (Q) exhibit very low hardness (down to 30% of hardness of base metal) in a very narrow area, less than 1 mm width immediately adjacent to the weld interface. The fracture location for weldments with bead-on plate varied between the fusion line and the base metal. However, the fracture location for weldments with bead-off plate was generally at the weld zone. SEM photographs shows that the base metal and the HAZ fracture are ductile whilst the weld metal and the fusion line fracture are the mixed rupture between ductile and brittle. The optimum mechanised MIG welding parameters having a low net heat input and a low porosity for 5 mm thick AA5083 butt-welds using ER5556A filler wire comprised a welding current of 270 amperes, a welding speed of 10.5 mm/s and a net heat input 603 J/mm. For weldments using ER5087 filler wire, the optimum welding parameters consisted of a welding current of 271 amperes, a welding speed of 10.7 mm/s and a net heat input 609 J/mm.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available