Chunzhong Liu

Effect of Mn and Fe on the Formation of Fe- and Mn-Rich Intermetallics in Al–5Mg–Mn Alloys Solidified Under Near-Rapid Cooling

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.

The Solidification Behavior of AA2618 Aluminum Alloy and the Influence of Cooling Rate

In AA2618 aluminum alloy, the iron- and nickel-rich intermetallics formed during solidification are of great effect on the mechanical properties of the alloy at both room temperature and elevated temperatures. However, the solidification behavior of the alloy and the formation mechanism of the intermetallics during solidification of the alloy are not clear. This research fills the gap and contributes to understanding the intermetallic of the alloy. The results showed that cooling rate was of great influence on the formation of the intermetallics. Under the condition of slow cooling, the as-cast microstructures of the alloy were complex with many coarse eutectic compounds including Al9FeNi, Al7(CuNi)5, Si, Al2Cu and Al2CuMg. The phase Al9FeNi was the dominant intermetallic compound, which precipitated at the earlier stage of the solidification by eutectic reaction L → α-Al + Al9FeNi. Increasing the cooling rate would suppress the formation of the coarse eutectic intermetallics. Under the condition of near-rapid cooling, the as-cast microstructures of the alloy consisted of metastable intermetallics Al9FeNi and Al2Cu; the equilibrium eutectic compounds were suppressed. This research concluded that intermetallics could be refined to a great extent by near-rapid cooling.

The Microstructures and Mechanical Properties of Al-5Mg-1.4Mn Alloy Cast under Near-Rapid Cooling

A high Mn content alloy (Al-5Mg-1.4Mn) has been cast under the condition of near-rapid cooling. The microstructures and mechanical properties of the alloy have been evaluated. The results indicated that under the condition of near-rapid cooling, the as-cast microstructures of the alloy consisted of α-Al matrix plus two types of intermetallics: Al6(Fe,Mn) and Mg2Si. The intermetallics were small and uniformly distributed. During hot and cold rolling, they broke into particles. The particle structures were dense, but small. Some cavities were observed among the Al6(Fe,Mn) fragments. Both the hot band and cold rolled sheet demonstrated excellent mechanical properties. The significant improvements were achieved by increasing Mn to a higher level, while being cast under the condition of near-rapid cooling.

The Influence of Cooling Rate and Alloying Elements on the Microstructure Refinement of Al‐5Fe Alloy

This research was focused on refining the microstructures of Al-5Fe alloy by increasing cooling rate during solidification and adding alloying elements. Under the condition of near-rapidly solidification, the primary Al13Fe4 phase was refined to the order of magnitude of 10 microns. Adding silicon to the alloy resulted in changes to the morphologies of the primary phase from starlike pattern to polygonal and firework-like patterns. The addition of silicon and cerium gave rise to further refinement in both primary and eutectic iron-rich phases to a significant extent.