Aluminium accounts for roughly 80% of EV battery pack enclosure construction today, with steel taking the remainder, per a 2025-09-16 review of pack materials in production [S1].
That dominance rests on a quantified mass advantage: aluminium enclosures are up to 50% lighter than equivalent steel designs, and aluminium-intensive cell-to-pack-ready tubs deliver over 20% mass reduction versus baseline aluminium extrusion concepts [S2]. A 90 kWh aluminium sheet enclosure from Novelis, introduced at a 50,000 units/year production cost target, was reported to add 6-10% to vehicle range versus heavier alternative structures [S3].
Mass and cost numbers driving the aluminium choice
An EV battery system typically measures about 2 m × 1.4 m and can weigh as much as 700 kg, representing 22-27% of total vehicle weight, with the housing and structure alone accounting for up to 20% of that mass and cost [S5]. The material trade is concrete: high-silicon steel is being designed into battery packs as a lower-fabrication-cost alternative to aluminium that can still meet crash performance targets, which is why steel has been 'fighting back' against aluminium in mid-market EV programmes [S1].
For an average pack weighing 500 kg, around 100 kg sits in the enclosure itself, and that figure is the lever the aluminium supply chain is competing over [S1]. Battery pack cost typically runs 30-50% of total vehicle cost, so enclosure mass and tooling decisions directly affect OEM platform economics [S1].
Extrusions vs sheet vs castings: a three-way comparison
Three forming routes compete for that 100 kg of enclosure mass, and the decision criteria split cleanly. Extrusions deliver long constant cross-section side rails and cross members, can double as leak-free liquid cooling channels, and supply crash energy absorption and torsional stiffness in a single section; the Mercedes EQS uses extrusions for its lightweight structural housing and perimeter cooling circuit, and the Audi e-Tron and Porsche Taycan also rely on extruded aluminium for their pack structures [S5]. Sheet-based aluminium tubs using grades like Novelis Advanz enable deep draws for complex bottom geometries, offer corrosion resistance, thermal management capability, and electromagnetic shielding, and are sized for cost efficiency at mass production volumes [S3].
Castings and stampings round out the option set: extrusions are the right call for long structural members with integrated cooling; sheet wins on deep-drawn complex bottom panels and lids at scale; castings suit localised high-load nodes. The cell-to-pack (CTP) trend favours sheet-intensive tubs with roll-formed frames and integrated thermal management bottom plates, because eliminating module housings removes mass that the enclosure must otherwise carry [S2].
Cooling integration and the thermal management angle
The most common solution for thermal management is a large aluminium cooling plate, often called a "cold plate," with intricate internal channels routed through the enclosure structure [S4]. Aluminium's high thermal conductivity is the key property here, and it is why extruded side rails double as cooling channels in packs like the Mercedes EQS and Audi e-Tron [S5].
For OEMs, this means enclosure material selection cannot be separated from cooling architecture: a steel enclosure has lower thermal conductivity, which reduces passive heat spreading and forces more active cooling, whereas aluminium's conductivity lets the structure itself share the thermal load [S1]. That is a real engineering lever, not a marketing claim, because the pack-level cold plate is part of the same BOM line item as the tub.
Sustainability, recycled content, and the policy push
European end-of-life vehicle legislation now requires the pack material to be recyclable, and OEMs want lower-carbon enclosure feedstock without sacrificing performance [S1]. Adding recycled aluminium into the enclosure mix significantly reduces carbon footprint without impacting mechanical performance, and Novelis' 95% recycled aluminium work in packaging demonstrates that the supply chain can hit very high recycled-content ratios when the value chain is aligned [S2].
On the supply side, tariffs on aluminium, steel, castings, extrusions, and stamped structures are pushing OEMs to localise enclosure sourcing and to redesign material flows around regional smelting and rolling capacity [S6]. This shifts the procurement question from "which grade of aluminium" to "which regional supplier can deliver Advanz-class sheet or large structural extrusions at the volumes a 200,000 vehicles/year programme requires" [S1][S6].
Where aluminium falls short and steel is re-entering
Aluminium's lower stiffness versus steel means reinforcement may be needed for crash loads, and fatigue plus crack propagation are a concern if the design is not carefully managed; aluminium is also more expensive than steel at equivalent strength [S1]. Steel enclosures, by contrast, offer high strength and excellent crash protection at lower cost, are easy to weld and form, and high-silicon steel grades reduce the carbon footprint while allowing thinner, lighter structures [S1].
For cost-sensitive mass-market programmes, high-silicon steel can match aluminium on crash safety at a fraction of the fabrication cost, which is why steel has been "fighting back" against aluminium in mid-market EV programmes [S1]. The practical takeaway: aluminium is the default where range, thermal integration, or CTP architectures dominate the spec; high-silicon steel is the rational pick where cost per kWh of pack is the binding constraint.
Standards, fire, and structural performance on the horizon
Fire protection and structural performance requirements are rising in parallel with cell energy density, with packs expected to protect occupants from intrusion and to maintain integrity under crush loads [S1]. Fire and intrusion testing continues to set thermal and structural benchmarks for enclosure material behaviour, and the standard test geometry for pack intrusion and side-pole crash continues to anchor the structural design rules [S1].
Composite thermoplastics, despite poor thermal conductivity unless hybridised, are now being used for large lids and bottom panels in mid- and even low-end designs, with Kautex Textron running large-scale thermoplastic manufacturing lines for this application [S1]. For buyers watching the next 12-24 months, the next signal to track is how quickly CTP aluminium sheet programmes reach 100,000 units/year run rates, and whether regional aluminium rolling capacity scales in step with OEM localisation strategies.
For the relevant spec sheets and selection criteria, see power supply, dc power supply, and switching power supply.
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