Low-Pressure Aluminum Casting for EV Battery Housings: When It Can Beat Die Casting

# Low-Pressure Aluminum Casting for EV Battery Housings: When It Can Beat Die Casting

Why battery housing design is driving a casting process rethink

An EV battery housing is a large, mostly flat aluminum structural part that needs to be leak-tight under sustained pressure, weldable without porosity burning through, dimensionally repeatable enough to mate with stamped lids and sealing gaskets over a 10+ year service life, and lightweight enough that every 1 kg reduction translates to real vehicle range. Until 2022-2023, most programs defaulted to either high-pressure die casting (HPDC) for small-to-mid housings or extrusion-plus-welding for large packs. In 2025-2026, several OEM programs have shifted toward low-pressure aluminum casting for the housing itself, because the process delivers a metallurgical and dimensional profile that the two traditional paths struggle to match at the volumes this segment now demands.

What low-pressure aluminum casting actually does differently

In low-pressure casting, molten aluminum is pushed upward from a sealed furnace into the mold cavity under controlled pressure — typically 0.3 to 1.0 bar. Compared to high-pressure die casting (where pressure is 700-1000 bar and fill times are measured in milliseconds), low-pressure fill is slow, laminar, and thermally controlled. The result is a metallurgical microstructure with lower gas porosity, lower oxide inclusion rate, and a denser dendritic structure in thick cross-sections. For an EV battery housing — which typically has thick cooling channels, thin skin sections for weight, and a continuous sealing flange — this matters enormously.

The three attributes where low-pressure may fit battery housings

Leak-tightness at scale. Battery housings often need a defined pressure or sealing check, but the test medium, pressure, hold time, and acceptance threshold should be confirmed by the buyer. HPDC parts, especially in thick sections at cross-overs, can exhibit trapped-gas porosity that only reveals itself under sustained pressure. Low-pressure casting can be a useful candidate when the RFQ requires slower fill, denser sections, documented inspection, and sealing-surface stability, but the expected yield and test plan must be quoted against the actual drawing.

Weldability. Most battery housings are either welded to a cooling plate or welded at the flange to a lid. Weld integrity depends on base-metal porosity — porosity near the weld zone releases gas under arc heat, creating pinholes in the weld bead. Pressure-tight casting standards require porosity below ASTM E155 Grade 2 in weld-prep zones, and low-pressure cast parts achieve this more reliably than HPDC at equivalent thickness.

Dimensional repeatability in large parts. A large battery housing can require flatness, sealing-rail, and interface checks that are more important than a generic casting tolerance class. Low-pressure casting may reduce some machining and stability risk for certain geometries, but the quote should state which surfaces are as-cast, which are machined, and which datums or CMM points control approval.

Where HPDC still wins

HPDC wins on cycle time and therefore on unit cost at very high volumes. If your battery program is at 200k+ units/year and the housing is small-to-medium (< 30 kg, < 800 mm), HPDC's 60-90 second cycle time vs low-pressure's 4-6 minute cycle gives a cost advantage that low-pressure cannot close. HPDC also dominates for thin-wall parts where the high-velocity fill is necessary to fill before solidification.

Where low-pressure can be the better RFQ route

Low-pressure wins for medium-to-large housings (500-1200 mm, 15-60 kg) at medium volumes (5k-80k units/year), where the cycle time penalty is affordable but the metallurgical quality premium is worth real dollars per part. This is exactly the band where most 2026 EV battery housing programs sit: volumes have ramped past prototype but not yet into extreme mass production, and the part is physically large enough that HPDC machines at those sizes require enormous tonnage and capital outlay.

What to ask a supplier quoting battery housing castings in 2026

Before awarding a battery housing program, a supplier should be able to answer these:

• •Which process — low-pressure, HPDC, gravity, or a hybrid — are you quoting, and why for this part geometry and volume?
• •What leak-test or sealing-surface inspection plan are you quoting, and at what sample rate?
• •Are your pressure-test and helium-leak inspection workflows documented and auditable?
• •For weld-prep zones, what porosity class per ASTM E155 are you certifying to?
• •What CT scan or X-ray sample plan do you run for the first 1000 parts of a new mold?
• •Can you reference a prior battery housing or fluid-handling housing program at similar volume, and share first-article inspection reports (anonymized if needed)?

The first two questions filter out suppliers who are quoting aggressively on price without engaging the metallurgical requirements. The last four separate production-ready suppliers from those who have run prototypes but not hit full-volume reliability.

What we do at Bohua

Bohua Casting runs low-pressure aluminum casting alongside gravity and die casting lines, giving us process-selection flexibility for medium-volume enclosure, rail, cover, and housing programs. For RFQ review, define the drawing revision, target volume, sealing surfaces, coating or masking scope, machining datums, and validation records needed. If your program is in the process-selection or RFQ stage, send a drawing and target volume for a process recommendation and a quote structure that separates tooling, part price, machining, coating, and inspection assumptions.