EV Battery Pack Housing Casting: Alloy & Leak-Test 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. For any Bohua RFQ, the alloy and casting route are selected only after drawing and requirement review; this article does not claim an approved battery-housing production program.

Leak Tightness and Porosity Limits

Battery housings are commonly leak-tested, and the acceptance criterion can be tight. An OEM or buyer specification may call for:

• •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 or a defined sampling plan, depending on the agreed project risk and control plan.
• •After final machining, because critical sealing surfaces are machined and porosity revealed by cutting can open a leak path.

The following is a generic buyer-side control-plan example, not a statement of Bohua's installed equipment or routine protocol:

• •Degassing verification at a frequency and by a method defined in the project control plan.
• •Shrinkage porosity control through gating, riser design, process review, and any agreed simulation or trial validation.
• •Critical sealing-surface regions designed with extra local thickness or directional solidification so last-to-freeze zones land outside the seal.
• •X-ray, CT, or another NDT method at an agreed launch and production frequency when the drawing or quality plan requires it.

If impregnation is proposed, buyers should define whether it is prohibited, conditionally allowed, or part of the approved process. The acceptance rule and evidence should be agreed before tooling rather than inferred from a generic yield target.

Bohua capability boundary: Bohua has its own pressure-tightness testing workshop. The test method, medium, pressure, duration, acceptance limit, and 100%-inspection-versus-sampling frequency are project-defined. Bohua does not claim an in-house helium leak-test system on this page. Confirmed supporting equipment includes a vacuum hydrogen analyzer and named X-ray inspection equipment; any additional method or capacity must be verified during RFQ review.

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.
• •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.
• •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.

Example Buyer Control Plan

The table below is an illustrative OEM or buyer requirement set. It is not Bohua's default control plan and should be replaced by project-specific, supplier-verified requirements during sourcing:

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.
• •Any required casting-simulation capability, software, ownership, and deliverables verified before award rather than assumed from a website claim.
• •Degassing and hydrogen-control methods documented at the project-defined frequency.
• •IATF 16949 certification with the scope explicitly covering casting, not only machining.
• •A detailed inspection plan aligned with the OEM control plan, including verified X-ray and leak-test capacity for the proposed volume and method.
• •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.