The transition has not occurred through the elimination of steel, but rather through its evolution and strategic integration alongside aluminium alloys, magnesium, advanced polymers, carbon fibre composites, structural adhesives, engineered foams, ceramic coatings, thermoplastics and hybrid laminates. Modern vehicles, particularly electric vehicles (EVs), now incorporate dozens of materially dissimilar systems within a single assembly, creating one of the most complex manufacturing ecosystems the automotive industry has ever encountered. Steel remains fundamental to automotive manufacturing because of its predictable crash behaviour, cost effectiveness and enormous manufacturing scalability. However, the steel used today bears little resemblance to the conventional mild steels that dominated vehicle manufacturing for decades. Ultra-high-strength steels (UHSS), advanced high-strength steels (AHSS), press-hardened boron steels and dual-phase steels now allow manufacturers to reduce section thickness while maintaining or significantly improving structural rigidity and occupant protection. These materials are extensively used in passenger safety cells, side intrusion beams, chassis rails and rollover structures where energy absorption and deformation management are critical. Yet despite these advances, the rise of electrification has exposed limitations in traditional steel-intensive construction. Battery electric vehicles carry substantial mass within the battery pack itself, often adding several hundred kilograms compared with equivalent internal combustion engine (ICE) vehicles. To offset this increase, manufacturers have aggressively pursued lightweighting strategies using aluminium and composite materials across body structures, suspension systems, closures and thermal management assemblies. Aluminium has become particularly prominent because it offers roughly one-third the density of steel while still providing excellent corrosion resistance and adequate structural performance when engineered correctly. It is now routinely found in bonnet assemblies, doors, subframes, crash structures, battery trays and suspension components. However, aluminium introduces its own engineering challenges, including galvanic corrosion when joined to steel, more complex repair methodologies and different crash energy absorption characteristics. Consequently, the industry has moved heavily toward mixed-material body architectures rather than wholesale material replacement. Where the industry is experiencing perhaps its most dramatic transformation is within EV battery enclosure design. Battery enclosures, sometimes referred to as battery packs, battery housings or battery trays, have evolved into some of the most technically sophisticated structural components within the modern vehicle. Historically, the underbody structure of a vehicle primarily provided torsional rigidity and occupant protection. In an EV, however, the battery enclosure becomes a multifunctional structural, thermal and safety-critical system simultaneously. It must contain and protect high-voltage battery modules, resist severe impact forces during collisions, manage vibration loads, provide environmental sealing against water and debris ingress, isolate electrical faults, dissipate heat and, increasingly, contribute directly to overall chassis stiffness. The challenge facing engineers is profound. Lithium-ion batteries generate substantial thermal loads during charging, discharging and high-performance operation. Thermal runaway events, while statistically rare, can propagate rapidly if heat is not effectively controlled. Consequently, battery enclosure design has become heavily focused on thermal management capability. Modern battery enclosures now incorporate highly engineered cooling pathways integrated directly into the enclosure structure itself. Many designs utilise liquid-cooled aluminium extrusions or cast cooling plates positioned beneath or between battery modules. Glycol-based coolant systems circulate through these channels to maintain narrow operating temperature windows essential for battery longevity, charging efficiency and safety stability. The enclosure materials themselves are also selected based on thermal conductivity characteristics. Aluminium remains highly favoured because it provides an effective balance between structural performance and heat dissipation. In some advanced EV architectures, manufacturers are experimenting with multi-layer composite sandwich structures that combine aluminium skins with thermally insulating or fire-resistant core materials. Certain systems now integrate ceramic barriers or intumescent materials capable of slowing thermal propagation during battery failure events.