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Title: The effect of heat treatment and microstructure on HAZ cracking in a 7XXX series aluminium alloy
Author: Waters, S.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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The effect of heat treatment and microstructure on liquation cracking in a 7XXX series aluminium alloy has been investigated using microstructural simulations in a Gleeble 1500 Thermomechanical testing machine. The work included analysis of instrumented 7017 aluminium alloy welds to assess their microstructural, mechanical and defect characteristics. Critical features of the crack sensitive white zone (WZ) were measured as a means of validating the microstructures simulated in the Gleeble facility. Four-point-bend fatigue testing was used to open the cracked welds and expose the surface of liquation cracks thereby allowing analysis of the localised chemical composition. Concentrations of zinc sufficient to cause liquation were identified in these regions. Simulations were executed on the basis of measured weld parameters. The validity of the generated microstructures were confirmed through grain size and microhardness measurements. The effect of time at peak temperature was also assessed and revealed typical solid state grain growth of recrystallised grains. Variation in peak temperature led to simulations of regions adjacent to the WZ, which have lower microhardness but no significant microstructural change. Such characteristics are typical of the over-aged zone seen in 7017 welds. Mechanical testing of the simulated WZ microstructure confirmed its reduced strength and hence, enhanced crack sensitivity. From this work recommendations concerning heat treatment and welding conditions have been made in order to help reduce the possibility of liquation cracking.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available