Abstract
Mn was an important alloying element used in Al–Mg–Mn alloys. However, it had to be limited to a low level (<1.0 wt %) to avoid the formation of coarse intermetallics. In order to take full advantage of the benefits of Mn, research was carried out to investigate the possibility of increasing the content of Mn by studying the effect of cooling rate on the formation of Fe- and Mn-rich intermetallics at different content levels of Mn and Fe. The results indicated that in Al–5Mg–Mn alloy with low Fe content (<0.1 wt %), intermetallic Al6(Fe,Mn) was small in size and amount. With increasing Mn content, intermetallic Al6(Fe,Mn) increased, but in limited amount. In high-Fe-containing Al–5Mg–Mn alloys (0.5 wt % Fe), intermetallic Al6(Fe,Mn) became the dominant phase, even in the alloy with low Mn content (0.39 wt %). Cooling rate played a critical role in the refinement of the intermetallics. Under near-rapid cooling, intermetallic Al6(Fe,Mn) was extremely refined. Even in the high Mn and/or high-Fe-containing alloys, it still demonstrated fine Chinese script structures. However, once the alloy composition passed beyond the eutectic point, the primary intermetallic Al6(Fe,Mn) phase displayed extremely coarse platelet-like morphology. Increasing the content of Fe caused intermetallic Al6(Fe,Mn) to become the primary phase at a lower Mn content.
Highlights
Al–Mg–Mn alloys AA5182 and AA5083 have found great applications in the automotive, marine, packaging, and construction industries due to their special characteristics, such as good weldability, ductility, toughness, formability, and corrosion resistance
It was thought that intermetallics with Chinese script morphology would have less harmful effects on the mechanical properties of the alloy
It was assumed that 657 °C and 653 °Ccorresponded to the precipitation of the primary intermetallic
Summary
Al–Mg–Mn alloys AA5182 and AA5083 have found great applications in the automotive, marine, packaging, and construction industries due to their special characteristics, such as good weldability, ductility, toughness, formability, and corrosion resistance. Finding a solution to refine the intermetallics during solidification was of great commercial interest for the production of the Al–Mg based aluminum alloys. A high-Mn-containing alloy with advanced mechanical properties could be developed and produced by using the CC process. Little investigation has been made on the formation and control of the intermetallics in high-Mn-containing Al–Mg–Mn alloy solidified under near-rapid cooling. This work investigated the intermetallics formed during solidification and the influence of Mn, Fe, and cooling rate on the formation of intermetallic Al6 (Fe,Mn) Their effect on the microstructures and mechanical properties of Al–5Mg–Mn alloys solidified under near-rapid cooling was reported elsewhere. The ultimate aim was to develop and produce a high-Mn-containing Al–Mg alloy with higher mechanical properties using the high productivity and low-cost CC process
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