The paper is proposing a mini-review on the capability of the new complex concentrated alloys (CCAs) to substitute or reduce the use of critical raw materials in applications for extreme conditions. Aspects regarding the regulations and expectations formulated by the European Union in the most recent reports on the critical raw materials were presented concisely. A general evaluation was performed on the CCAs concept and the research directions. The advantages of using critical metals for particular applications were presented to acknowledge the difficulty in the substitution of such elements with other materials. In order to establish the level of involvement of CCAs in the reduction of critical metal in extreme environment applications, a presentation was made of the previous achievements in the field and the potential for the reduction of critical metal content through the use of multi-component compositions.

Lightweight complex concentrated alloys (LWCCA), composed of elements with low density, have become a great area of interest due to the high demand in a large number of applications. Previous research on LWCCAs was focused on high entropy multicomponent alloy systems that provide low density and high capability of solid solution formation. Present research introduces two alloy systems (Al-Cu-Si-Zn-Mg and Al-Mn-Zn-Mg-Si) that contain readily available and inexpensive starting materials and have potential for solid solution formation structures. For the selection of appropriate compositions, authors applied semi-empirical criteria and optimization software. Specialized modeling software (MatCalc) was used to determine probable alloy structures by CALPHAD, non-equilibrium solidification and kinetic simulations. The selected alloys were prepared in an induction furnace. Specimens were heat treated to provide stable structures. Physicochemical, microstructural, and mechanical characterization was performed for the selected alloy compositions. Modeling and experimental results indicated solid solution-based structures in the as-cast and heat-treated samples. Several intermetallic phases were present at higher concentrations than in the conventional alloys. Alloys presented a brittle structure with compression strength of 486–618 MPa and hardness of 268–283 HV. The potential for uniform intermetallic phase distribution in the selected alloys makes them good candidates for applications were low weight and high resistance is required.

Complex concentrated alloys (CCAs) are new types of materials, where the equimolar rule proposed by high entropy alloys (HEAs) is modified in relation to the potential of the obtained structures. CCAs expend the compositional space of the conventional alloys, revealing new pathways for material design. The Al₇Cu_0.2Si_0.2Zn_0.2Mg_0.1 alloy was prepared in an induction furnace, in controlled atmosphere and was cast in a copper ingot mold. The resulting samples of Al₇Cu_0.2Si_0.2Zn_0.2Mg_0.1 were analysed by chemical, structural, and corrosion resistance. Furthermore, the alloy has been subjected to mechanical tests of hardness, elongation and tensile strength. The corrosion immersion tests were performed in 3wt% and 5wt% NaClsolution, and corrosion indices were measured periodically. The obtained corrosion film was analized by SEM-EDS to determine the composition and structural behaviour. Depending on the adhesion level, the corrosion film remained stable or partially broken and separated in the solution. The sample weight loss presented large variations between the various experimental conditions, but the general tendency was the decrease in the weight of the samples during the corrosion tests. The formation of oxide and chloride layers, during the corrosion process, determined only the dealloying in Al. Other elements remained in initial concentrations. Overall, the resistance of the alloy in saline environment seems to be promising, with significant improvement over the comparable compositions of 2000 and 7000 series aluminium alloys.