Aluminium Alloy Castings

What is gravity die casting?

Gravity die casting — also known as permanent mould casting — uses a reusable steel mould into which molten aluminium is poured under gravity. Unlike sand casting, the permanent mould produces a consistent, fine-grained surface finish and tighter dimensional repeatability across production runs. Unlike high-pressure die casting, it is well suited to thicker-walled, pressure-bearing components where pressure-tight internal soundness is critical.

For aluminium parts that require PED compliance, pressure tightness or structural integrity, gravity die casting offers the best balance of dimensional accuracy, mechanical properties and cost at low-to-medium volumes. Parts are typically heat-treated after casting to achieve the required temper — T5 or T6 for most structural and pressure applications.

Choosing the right aluminium casting process

Gravity die casting is the right process for pressure-bearing, thicker-walled aluminium components requiring PED 2014/68/EU compliance, good mechanical properties after heat treatment, and medium production volumes. Minimum wall thickness is typically 3–4 mm.

For high-volume, thin-wall, non-pressure aluminium components (housings, brackets, heat sinks, enclosures), aluminium high pressure die casting → is the appropriate process. HPDC is not used for PED-certified pressure-bearing parts.

Aluminium alloys we cast

We routinely cast the principal EN 1706 gravity die alloys and their international equivalents, including:

• LM25 (AlSi7Mg / EN AC-42000) — the most widely used pressure casting alloy; excellent strength after T6 heat treatment; suited to pumps, valve bodies and structural housings. The closely related A356 (EN AC-42100) is supplied where its tighter chemistry (lower Fe) is specified.
• LM6 (AlSi12 / EN AC-44100) — outstanding corrosion resistance and pressure tightness; preferred for marine, food-grade and thin-section applications
• LM9 (AlSi10Mg / EN AC-43000) — good pressure tightness and castability; used for hydraulic and pneumatic components
• LM4 (AlSi5Cu3 / EN AC-45400) — general purpose alloy with good machinability

Other alloys and bespoke chemistries can be sourced to your specification. Full chemical and mechanical certification is supplied with every batch, issued against EN 1706, ASTM B26 or equivalent as required.

Sizes, tolerances and finish

Single-piece weight	From 2 kg up to 20 kg within PED approval scope
Linear tolerance (as-cast)	Typically CT6–CT7 (ISO 8062) on gravity die features
Surface finish	Ra 6.3 µm or better on most as-cast surfaces
Wall thickness	3 mm minimum typical; up to 30 mm within PED PMA approval scope (not a process capability limit)
Diameter	Up to 350 mm within PED approval scope
Heat treatment	T5, T6 or T7 tempers available; solution treatment and ageing in-house
Machined features	Held to drawing tolerance via CNC milling, turning and drilling

PED compliance for aluminium pressure castings

Aluminium alloy castings used in pressure equipment — pump housings, valve bodies, compressor components, fluid manifolds — must comply with the Pressure Equipment Directive 2014/68/EU where the equipment falls within its scope. Our partner foundries hold PED certification for aluminium gravity die castings, and we can supply the documentation required to satisfy your CE marking obligations. PED explained →

PED compliance for aluminium castings typically requires:

• Foundry approval under Particular Material Appraisal (PMA) per PED Annex I §4.3 — the route by which a notified body assesses the foundry's material, melt practice and quality system for pressure-bearing service
• Chemical and mechanical testing of every production batch
• Traceability from melt to finished part
• Material certification to EN 10204 3.1 (or 3.2 with notified-body witness where required)
• Non-destructive testing where specified by the applicable standard or customer

We manage the full documentation package and ship certified parts on a DDP basis. You receive the casting and its paperwork together — ready for your own inspection and CE marking records.

Quality, testing and certification

Every pressure-bearing aluminium casting is produced and inspected to a defined quality plan. Standard capabilities include:

• ISO 9001:2015 quality management system
• TÜV Rheinland (Notified Body ID-No. 0035) approval for gravity die aluminium castings in EN AC-42000 (EN 1706, T6) 2–20 kg under Directive 2014/68/EU Annex I point 4.3 — certificate no. 01 202 CHN/Q-24 0010.00
• Chemical analysis by optical emission spectrometer on every melt
• Mechanical testing — tensile strength, proof stress, elongation and Brinell hardness
• Dimensional inspection on coordinate-measuring machine (CMM)
• Non-destructive testing — dye penetrant (PT) and radiographic (RT) on request
• Pressure testing — hydrostatic and pneumatic at end-of-line
• Full material and inspection certification (3.1 / 3.2 EN 10204) supplied with every shipment

Industries and applications

Our aluminium alloy castings are used across demanding industrial sectors:

• Pumps and fluid handling — impeller housings, volute casings, manifolds, end covers
• Compressors and pneumatics — cylinder heads, valve plates, bodies
• Marine — sea-water resistant housings, brackets and fittings in LM6
• Industrial machinery — OEM housings, gearbox covers, bearing carriers
• Renewable energy — structural and fluid-handling components for wind and hydrogen systems
• Oil and gas — instrument housings, junction boxes and low-pressure flow components