EV Battery Pack Housing Aluminum Casting Requirements: A Supplier-Side Engineering Guide

# EV Battery Pack Housing Aluminum Casting Requirements: A Supplier-Side Engineering Guide

EV battery pack housing aluminum casting has become one of the most demanding applications in modern foundry work. The part has to be pressure-tight, crash-worthy, weldable to stamped or extruded structures, dimensionally stable over a large footprint, and delivered at a cost that survives an OEM's procurement review. Most castings asked to do two of those things well; battery housings ask for all five simultaneously. This guide walks through the technical requirements that matter for buyers and quality engineers evaluating a supplier, written from the perspective of a foundry that quotes these parts.

If you are still at the alloy-shortlisting stage, the A356 vs ADC12 alloy selection guide covers the underlying trade-offs in casting process, mechanical properties, and cost. For a sourcing package, the aluminum casting RFQ information checklist explains what data to include so quotes come back accurate the first time.

Why Battery Pack Housings Drive Unusual Casting Requirements

A battery pack housing is not simply a large tray. It performs at least five functions in a single part:

• •Structural carrier for cell modules — must hold module weight (often 300-600 kg for passenger EVs) through road-load fatigue cycles without distortion or resonance.
• •Crash load path — in a side-pole or side-barrier impact, the housing participates in energy absorption and must prevent intrusion into the cell stack.
• •Environmental barrier — typically IP67 or IP6K9K sealing, protecting cells from water, dust, and salt spray.
• •Thermal interface — houses or interfaces with the cooling plate, so the wall thickness and surface flatness affect thermal contact and therefore cell temperature uniformity.
• •Weld and bolt partner — joins to stamped lids, extruded frames, cooling plates, and vehicle floor structures via MIG, friction stir welding (FSW), or mechanical fasteners.

Each function pulls the design in a different direction, and the casting supplier ends up negotiating the trade-offs.

Alloy Selection: Why AlSi7Mg (A356/A357) Wins Most Battery Programs

The dominant alloy family for gravity and low-pressure cast battery housings is AlSi7Mg, covering A356, A356.2, A357, and their regional equivalents. Three reasons:

• •Weldability. Unlike high-iron secondary alloys (ADC12/A380), primary AlSi7Mg welds reliably with ER4043 or ER4047 filler. Battery housings almost always need welded lids or cooling plate joints.
• •T6 mechanical properties. After solution and aging, A356-T6 reaches ~240 MPa UTS and ~170 MPa YS with 6-8% elongation. That elongation matters for crash load cases where the housing must deform without fracturing.
• •Low hydrogen susceptibility in controlled foundries. With rotary degassing to below 0.15 ml/100g, porosity can be kept low enough for leak test acceptance without requiring impregnation.

ADC12 and A380 high-pressure die castings are sometimes used for smaller pack housings where cost dominates and the lid/frame joint is bolted rather than welded. For gigacasting-scale integrated structural castings, alloys like Castasil-37 and AlSi10MnMg (Silafont-36 family) are more common because they are heat-treatment-free and designed for vacuum-assisted HPDC. Bohua's practice on battery housings is AlSi7Mg with gravity or low-pressure die casting — optimized for weldability and elongation over raw cycle time.

Leak Tightness and Porosity Limits

Battery housings are leak-tested, and the acceptance criterion is tight. A typical spec looks like:

• •Air decay or helium leak test at 30-50 kPa, leak rate < 5 x 10^-3 mbar·L/s (helium) or equivalent in air decay.
• •100% part inspection, not sample-based.
• •After final machining, because critical sealing surfaces are machined and porosity revealed by cutting can open a leak path.

Translating this to foundry control:

• •Degassing verified on every shift by reduced pressure test (RPT) or AlScan.
• •Shrinkage porosity controlled by gating and riser design plus simulation (MAGMAsoft, FLOW-3D) — not by post-casting impregnation as a safety net.
• •Critical sealing-surface regions designed with extra local thickness or directional solidification so last-to-freeze zones land outside the seal.
• •100% X-ray or CT on the first dozen parts of a new program to verify internal quality before leak testing.

If a supplier routinely relies on vacuum impregnation to pass leak test, that is a red flag for a long-term program. Impregnation is acceptable as a contingency on mature parts, but a well-engineered battery housing should pass leak test without it on well over 99% of the population.

Dimensional Control on a Large Footprint

Passenger-car battery housings commonly span 1,500-2,000 mm in length. A general casting tolerance class like ISO 8062 DCTG 8-10 applied over that length produces absolute tolerances of ±2-4 mm on cast dimensions, which is too loose for module location and cooling-plate interface. Real programs handle this with:

• •Cast-then-machine approach on all critical sealing and mating surfaces. Casting tolerances apply only to non-functional surfaces.
• •#0f1e3d]">Fixture datum strategy defined early — the CMM and machining fixtures use the same 3-2-1 datum scheme to avoid cumulative drift. Our [CMM inspection requirements for cast aluminum parts post covers datum strategy in detail.
• •Stress-relief heat treatment after rough machining for large thin-wall housings to control residual stress distortion before finish machining.
• •Fixture gauges rather than free-state CMM for high-volume check of module-bay flatness and cooling-plate seat profile.

Crash Load Cases and Why Elongation Matters

US FMVSS 305 and UN ECE R100 do not prescribe a specific material property target, but OEM internal standards translate side-pole and side-barrier intrusion requirements into housing-specific load cases. A typical target is to keep cell intrusion under 20 mm at a specified barrier velocity. The housing must deform plastically without fracture at the impact zone and without tearing at welded joints.

That drives two casting requirements:

• •Minimum elongation of 5-7% at the cast-and-T6 condition — not average but 3-sigma lower bound. Hydrogen porosity depresses elongation, so degassing discipline is a structural requirement.
• •Weld-line control in simulation and gating so that last-to-fill fronts do not land in the crash load path. Cold-shut-prone regions should be designed out, not inspected out.

Suppliers should be willing to share tensile test data by location (coupon cut from representative crash zones), not just separately-cast test bars, because separately-cast bars overstate the elongation available in the actual part wall.

Weldability and Joint Design

Most pack housings are not a single casting — they are a cast tray welded to a stamped or extruded frame, or bolted to a cast lid. The casting-side requirements:

• •Hydrogen content below 0.15 ml/100g at pour. Higher hydrogen shows up as weld-bead porosity during fusion welding.
• •Iron content controlled. AlSi7Mg targets Fe < 0.15% for primary-grade material. Higher Fe in secondary alloy reduces weld integrity and ductility.
• •Weld prep surfaces machined to remove the cast skin and any embedded oxide. Weld directly on a cast surface is possible but yields inconsistent results.
• •#0f1e3d]">FSW compatibility if the OEM uses friction stir welding for the cooling plate joint. FSW on cast AlSi7Mg is well-characterized — see the [ASM Handbook Vol 6A: Welding Fundamentals and Processes for published joint properties and parameter windows.

Inspection Protocol That OEMs Actually Require

A representative control plan for a production battery housing:

This is heavier inspection than a non-safety-critical casting and should be priced in from the start. A supplier quoting a battery housing at the same inspection cost as a generic pump body is either under-scoping the program or planning to cut corners.

What to Verify Before Awarding the Business

Before signing a purchase order for a battery housing program, a buyer should confirm:

• •Prior experience with a structural, leak-tight casting of similar size and wall thickness — not just "aluminum casting experience" in general.
• •Casting simulation capability in-house (MAGMAsoft, FLOW-3D, or ProCAST) and a willingness to share simulation output during DFM review.
• •Rotary degassing with documented per-shift RPT and hydrogen targets.
• •IATF 16949 certification with the scope explicitly covering casting, not only machining.
• •A detailed inspection plan aligned with the OEM control plan, including X-ray and leak-test capacity to handle program volume.
• •Tensile data from part-cut coupons, not only separately-cast bars.

Battery pack housings reward suppliers who treat the part as a structural, safety-critical assembly from day one, and punish suppliers who treat it as a large bracket. The difference shows up first in leak-test yield, then in weld integrity, and eventually in warranty claims that can cost more than the entire program margin.