Non-Equilibrium Crystallization of Aluminium alloys with transition metals
It is very well known that the mechanical properties of Al alloys can be enhanced up to 20% by better control of the microstructure formed during the casting process, which is particularly important for the automobile industry. This fact has led to a good amount of research to understand and model the factors influencing the microstructure of the alloys. Transition metals have been used as the main alloying elements in commercial aluminium alloys for many years now as they often improve the formability due to grain refinement and resistance to different types of corrosion, etc. But, many questions remain unanswered about how the various phases containing these elements are formed.
All of the principal alloying elements form eutectic phase diagrams with aluminum. The rapid solidification of these alloys leads to an increase in the concentration of these alloying elements in the terminal solid solutions and is accompanied by both the formation of metastable phases. In such cases solidification is controlled by phase selection. In the present scientific research work, our goal is to study the formation of different metastable phases during non-equilibrium crystallization in Aluminium-transition metal based alloys and the effect of cooling rate on their formation. This will be achieved by using techniques of SEM, DTA, XRD and TEM.
The solidification of Al-rich Al-Mn alloys (3.5%, 4% & 4.5% wt) and Al-rich Al-Mn-Cu (9 alloys with 1%-5% wt Mn & Cu content) has been studied both experimentally and by calculation of the phase equilibria using Thermo-Calc software. The addition of manganese to aluminum increases strength and improves strain hardening while not appreciably reducing ductility or corrosion resistance. For Al-Mn system, the results of the previous studies which indicated that one or more stable intermetallic phases get suppressed on solidification, have been confirmed. It was shown that in Al-Mn system, it is important to consider the formation of Al11Mn4 even though other intermetallic phases have a higher driving force for solidification. It was also shown that the formation of metastable phases increases the solubility of Mn in Al solid solution. For Al-Mn-Cu system, SEM results show the formation of ternary phases in the Al rich region. There’s not enough research work that has been done on the Al rich side of the phase diagram. So, one of the tasks is to analyze and construct the phase diagram data for this part of the phase diagram and analyze the formation of all possible ternary phases.
Supervisor- Prof Vadim S. Zolotorevskiy