Increasing use of aluminum alloys in the automotive industry increases the importance
of the production of sheet aluminum. To provide cost effective sheet aluminum to the
industry, twin-roll casting (TRC) is becoming more important compared to DC casting.
Demand for usage of different aluminum alloys in sheet form introduces some
difficulties that should be considered during their applications. The main problem
encountered during the welding of aluminum alloys is hot cracking. The aim of this
study is to understand the difference in hot cracking susceptibility of two twin roll cast
(TRC) aluminum-magnesium alloys (5754 and 5049 alloys) during welding. Varestraint
test method was used to evaluate the effect of welding parameters, strain levels, filler
alloys and mid-plane segregation on hot cracking susceptibilities.
Hot cracking susceptibility of both 5049(Al-2wt%Mg) and 5754(Al-3wt%Mg) alloys
increased with increasing strain level. Also, it was observed that hot cracking
susceptibility was higher for the alloy having higher magnesium content. Thermal
analysis results verified that hot cracking susceptibility indeed can be related to the
v
solidification range. As is suggested in the solidification range approach, the results of
the present study confirm that the extent of solidification and liquation cracking depend
on the magnitude of solidification range and the strain imposed during welding. Hot
cracking susceptibility of 5754(Al-3wt%Mg) alloy has shown slightly decreasing
behavior with addition of 5356 filler alloy. On the other hand, addition of 5183 filler
alloy has increased solidification cracking susceptibility of two base alloys. The fracture
surfaces of liquation and solidification cracks were investigated by scanning electron
microscope with EDS. Liquation crack surfaces of the 5754(Al-3wt%Mg) alloy were
found to have high Mg and Si content. For the 5754(Al-3wt%Mg) alloy, a quench test
was designed to observe the effect of mid-plane segregation zone. It was observed that
there was a eutectic reaction resulting in formation of liquid phase below solidus
temperature of 5754(Al-3wt%Mg) alloy. Moreover, internal cracks have formed at the
mid-plane segregation zone after Varestraint test. Results show that 5049(Al-2wt%Mg)
alloy should be chosen compared to 5754(Al-3wt%Mg) alloy for welding. Moreover,
low line energy should be applied and filler alloys with high magnesium content should
be used during welding to decrease hot cracking tendency of welds.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/2/12611202/index.pdf |
| Date | 01 October 2009 |
| Creators | Tirkes, Suha |
| Contributors | Ankara, Alpay |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for METU campus |
Page generated in 0.003 seconds