**7. Development of Al-Cu-Mn-Zr alloy**

As mentioned before, age hardening Al-Cu alloys faces significant precipitate coarsening, which restricts their use for high temperature applications [48]. Numerous attempts have made over the years to increase the operational temperature for Al-Cu alloys; the most successful approach was by trace addition of various elements like Sc and Zr [49]. Micro-alloying improves the high temperature stability in two distinct ways:


The classical approach for developing any new alloy system relies on the age-old trial and error method which has serious drawbacks, primarily considering the resource constrains and added cost from industrial standpoints [55, 56]. A more state of the art strategy of alloy designing is by using integrated computational materials engineering (ICME) approach [57, 58]; a successful example of this is realized in the development of Al-Cu-Mn-Zr alloys. The key components of ICME approach for the development of this alloy system are: (a) thermodynamic and kinetic approximations for stability of precipitates against growth controlling mechanism/s, (b) appropriate modeling for assessment of thermo-physical and thermo-mechanical properties from existing phases, (c) simulation and model/s to predict defect formation during casting processes, (d) models for prediction of microstructure during casting and other thermo-mechanical processing operations, (e) models for property prediction from microstructure and defect structure evolution, and (f) models for manufacturing of components at in-service conditions [59, 60].

These above mentioned steps were followed in the development of Al-Cu-Mn-Zr alloys which was primarily aimed to replace traditional Al-Si and Al-Si-Cu alloys in automotive applications (e.g. cylinder heads in passenger vehicle engines) [59]. Firstly, thermo-physical and thermo-mechanical properties for casting process

simulation were obtained from thermodynamic databases. The simulation of casting process was conducted to estimate the casting defects and as-cast microstructure. Afterwards, thermodynamic models were employed for optimization of heat treatment cycle in terms of desired precipitation sequence, precipitate growth etc. This helped to estimate the spatial variation of thermo-physical properties over the component scale as well. Finally, component level properties e.g. residual stress, fatigue performance etc. were evaluated in order to estimate the in-service performance of the alloys considering the above mentioned parameters [61].
