Magnesium Die Casting: Process, Alloys, Design and Cost Guide

Magnesium die casting is used to manufacture lightweight metal components with complex geometry, thin walls and repeatable dimensions. It is especially valuable when a product needs a better strength-to-weight ratio than many plastics and a lower mass than comparable aluminum or zinc parts.

This guide explains the magnesium die casting process, common alloys, design rules, achievable quality, surface finishes, tooling, cost and supplier selection. It is written for engineers and buyers preparing a new casting project.

What Is Magnesium Die Casting?

Magnesium die casting forces molten magnesium alloy into a hardened steel mold under high pressure. The metal fills the cavity rapidly, solidifies and is ejected as a near-net-shape component. Gates, runners and overflow material are then removed.

The process can integrate ribs, bosses, mounting features, shielding structures and cosmetic surfaces into one part. Secondary machining and finishing are added only where the design requires them.

Why Use Magnesium?

• Low density for lightweight products

• Good strength-to-weight and stiffness-to-weight performance

• Excellent castability for complex, thin-wall geometry

• Good machinability for precision secondary features

• Useful vibration and impact energy absorption

• Electromagnetic shielding for electronic housings

• Potential to consolidate several components into one casting

• Recyclability within a controlled metal supply chain

Common Applications

Magnesium castings are found in automotive structures, steering and seat components, power-tool housings, camera bodies, laptop frames, communication equipment, medical devices and portable consumer products.

The best applications benefit from both low mass and integrated geometry. Replacing a multi-piece stamped, machined or molded assembly can reduce fasteners, handling and assembly operations.

Magnesium Die Casting Process

1. Review the CAD model, drawing, alloy, volume and service requirements.

2. Complete DFM for wall thickness, draft, parting line, gates and ejection.

3. Design and manufacture the production die and trim tooling.

4. Prepare the alloy and establish controlled casting parameters.

5. Inject metal into the die, solidify and eject the casting.

6. Trim runners, gates, overflows and flash.

7. Machine, finish and assemble features where required.

8. Inspect the approved characteristics and package the parts.

Hot-Chamber vs Cold-Chamber Casting

Magnesium alloys may be processed in hot-chamber or cold-chamber machines, depending on alloy, part size and production requirements. Hot-chamber equipment places the injection system in the molten metal and can provide short cycles for suitable parts.

Cold-chamber equipment transfers a measured quantity of metal into a separate shot sleeve. It is used when machine size, alloy or process design makes that method preferable. The supplier should select the process around quality and capacity rather than a generic rule.

Common Magnesium Die Casting Alloys

AZ91D vs AM60B

AZ91D is a common general-purpose choice because it offers good casting behavior, mechanical properties and finish compatibility. It is frequently used for electronic housings, tools and industrial products.

AM60B is often selected when ductility, impact behavior and crash performance are more important. Final selection should follow the applicable standard, service temperature, corrosion environment and validation plan.

How to Select a Magnesium Alloy

Start with tensile load, impact, stiffness, operating temperature, corrosion exposure and finishing needs. Then consider casting method, wall thickness and available supplier experience.

State the exact alloy and standard on the drawing. If a substitute is proposed, compare chemistry, mechanical properties, creep behavior, corrosion resistance and processing history before approval.

Magnesium vs Aluminum Die Casting

Magnesium vs Zinc Die Casting

Magnesium is much lighter than zinc and is attractive for portable or transportation products. Zinc offers excellent fine-detail filling, long tool life and a solid feel, but its higher density increases part mass.

The correct comparison includes geometry, mechanical loading, finish, cycle time and total assembly design. A lighter material does not automatically produce the lowest-cost or strongest product.

Magnesium Die Casting vs Injection Molding

Plastic injection molding can produce lighter parts with insulation and broad color options. Magnesium provides metallic stiffness, heat transfer, electromagnetic shielding and improved dimensional stability in many structural housings.

Compare the full assembly. A magnesium casting may eliminate inserts, shielding layers or reinforcement, while plastic may reduce material and finishing cost for less demanding loads.

Design for Manufacturability

Early DFM should review the load path, wall thickness, draft, ribs, bosses, radii, parting line, undercuts, gates, overflows and ejectors. Machining, coating and assembly must be considered at the same time.

A casting supplier should return a marked-up design showing mold direction, slides, critical tool steel conditions and visible process marks before die manufacturing begins.

Wall Thickness

Magnesium fills thin sections well, but minimum wall thickness depends on flow distance, projected area, alloy, machine capability and feature layout. Uniform walls normally fill and cool more consistently than abrupt thick-to-thin transitions.

Core out heavy masses and use ribs where stiffness is required. Local thick areas can increase shrinkage, porosity and cycle time without providing efficient structural performance.

Draft Angles

Draft helps the casting release from the die without dragging or distortion. Internal walls, deep pockets and textured surfaces generally need more draft than short external faces.

Do not remove draft merely to match a nominal CAD shape. If a functional surface cannot accept draft, discuss machining or a tool action during DFM.

Ribs and Bosses

Ribs add stiffness without making the main wall unnecessarily thick. Keep rib networks open enough for metal flow and blend intersections with radii.

Bosses support fasteners, bearings and alignment features. Thin isolated bosses may fill poorly, while heavy boss bases can create hot spots. Connect them to nearby walls with balanced ribs.

Fillets and Radii

Rounded transitions improve flow, reduce stress concentration and protect the die from fragile sharp steel. Internal corners should have practical radii, especially near ribs, bosses and deep pockets.

Consistent radii simplify tooling and finishing. Critical mating edges can be machined when a sharp functional condition is unavoidable.

Parting Lines and Ejector Marks

The parting line determines how the tool opens and where flash or mismatch may appear. Ejector pins leave small circular witnesses on the casting.

Keep both away from important cosmetic and sealing surfaces when possible. Identify appearance zones on the drawing so the tool designer can place unavoidable process marks deliberately.

Undercuts and Slides

Side holes, hooks and reverse features can require slides or other movable actions. These increase die cost, maintenance and cycle time.

Consider moving a feature into the main opening direction, drilling it later or redesigning the assembly. A simpler tool usually provides better uptime and repeatability.

Gate, Runner and Overflow Design

The feed system must fill the cavity rapidly while controlling turbulence and air entrapment. Gate thickness, direction and location influence weld regions, appearance and trimming.

Overflows collect the first or colder metal and support venting. Gate and overflow vestiges should be placed where trimming will not damage functional or cosmetic zones.

Venting and Vacuum Assistance

Air must escape as metal enters the cavity. Poor venting can cause porosity, incomplete fill, surface defects and reduced mechanical performance.

Vacuum-assisted die casting can reduce trapped gas for demanding parts, but it does not correct unsuitable geometry or unstable processing. Vent design, metal handling and shot control must work together.

Dimensional Tolerances

Achievable tolerance depends on part size, die temperature, feature location, cavity count and whether a dimension crosses the parting line or a slide. Dimensions formed in one die half are usually easier to control.

Use functional tolerances rather than applying tight limits to every feature. Establish datums, gauge methods and capability expectations before tooling approval.

Porosity and Leak Tightness

Gas and shrinkage porosity can occur in pressure cast components. Risk increases in thick sections, isolated masses and poorly vented flow paths.

If the part must contain fluid or gas, define the medium, pressure, test duration and allowable leak rate. Vacuum impregnation may be considered, but the casting and test strategy should be developed first.

CNC Machining Magnesium Castings

Machining is used for precision bores, sealing faces, threads and assembly datums. Magnesium cuts efficiently, but chips require suitable collection and fire-safety procedures.

Fixtures must support thin walls without distortion. Use stable cast datums and enough machining allowance to clean the surface while avoiding excessive removal that could expose internal porosity.

Surface Finishes

Possible finishes include conversion coatings, paint, powder coating, electrophoretic coating and specialized plating systems. The finish must be compatible with the alloy, corrosion environment and appearance requirement.

Mask electrical contacts, threads and precision fits. State coating thickness, color, gloss and adhesion testing on the drawing or purchase specification.

Corrosion Protection

Modern high-purity magnesium alloys can perform well when casting quality, cleaning and coating are controlled. Galvanic contact with dissimilar metals must still be considered, especially in wet or salt environments.

Use compatible fasteners, barriers, sealants or isolation washers where required. Drainage and avoidance of water traps are part of the product design, not only the coating specification.

Quality Control

• Verify alloy chemistry and incoming metal records

• Monitor melt, die and process parameters

• Inspect first-off samples and critical dimensions

• Use gauges, CMM inspection or scanning as appropriate

• Evaluate porosity in defined functional zones

• Test coating thickness, adhesion and corrosion resistance

• Perform leak, torque, load or assembly tests where required

• Maintain cavity, batch and production traceability

Common Magnesium Die Casting Defects

Magnesium Die Casting Tooling

The production die includes cavity and core inserts, runners, gates, vents, cooling circuits, ejectors and any slides. Tool construction must withstand thermal cycling and high injection pressure while preserving dimensional stability.

Ask the quotation to define tool steel, cavity count, expected life, spare inserts, trim tooling, ownership and maintenance. A low initial tool price can be misleading if essential scope is excluded.

Tool Maintenance

Preventive maintenance includes cleaning vents, inspecting slide wear, monitoring ejectors, checking cooling channels and repairing parting surfaces. Production data can reveal gradual tool deterioration before it creates a major quality issue.

Keep cavity-specific measurement records and approved appearance samples. Validate dimensions and coating quality after significant repair.

Magnesium Die Casting Cost

Total cost includes engineering, die manufacturing, trim tooling, trials, alloy, machine time, trimming, machining, finishing, inspection, packaging and freight. Part complexity and quality requirements often matter more than raw metal price alone.

Tooling is a significant upfront investment, but unit economics improve when repeat volume spreads that cost over more parts. Compare total landed assembly cost, not only the casting price.

Factors That Affect Unit Price

• Part weight and alloy

• Projected area and machine size

• Cycle time and cavity count

• Slides and complex tool actions

• Trimming and deburring

• CNC machining operations

• Coating and cosmetic requirements

• Inspection, testing and documentation

• Annual order volume and packaging

Lead Time

A typical schedule includes DFM, die design, steel procurement, machining, assembly, first trial, dimensional correction and finish validation. Complex tools and cosmetic coatings need additional iterations.

Agree on milestones for DFM approval, tool design release, first samples and production approval. Fast, complete engineering feedback helps protect the schedule.

Prototype Options Before Tooling

CNC machining, metal additive manufacturing and prototype casting can be used to evaluate fit and function before production tooling. Each method has different material, porosity and surface characteristics.

Use prototypes to answer specific questions, then validate final mechanical, coating and assembly performance with production-intent die cast samples.

How to Choose a Magnesium Die Casting Supplier

Look for demonstrated experience with the selected alloy, wall thickness, part size and finish. The supplier should be able to coordinate die design, casting, machining, coating, assembly and inspection.

Review process controls, material traceability, dimensional equipment, corrosion testing and fire-safety practices. Ask for examples of comparable parts rather than relying on a general capability statement.

RFQ Checklist

• 3D CAD model and dimensioned drawing

• Specified magnesium alloy and standard

• Annual volume and lifetime quantity

• Critical dimensions, datums and capability needs

• Mechanical load and operating temperature

• Corrosion environment and coating specification

• Leak, torque or functional test requirements

• Machining and assembly scope

• Inspection reports and material certificates

• Packaging and delivery location

Frequently Asked Questions

Is magnesium die casting lighter than aluminum?

Yes. Magnesium has a lower density than aluminum, so an equal-volume component is lighter. The final product comparison must also consider required wall thickness, ribs, loads and assembly design.

Is magnesium die casting strong?

Magnesium alloys provide useful strength and stiffness at low weight. Performance depends on alloy, geometry, casting quality, temperature and load direction, so critical parts require application-specific validation.

Can magnesium die castings be painted?

Yes. Proper cleaning, pretreatment and a compatible coating system can provide color and corrosion protection. Masking and coating thickness should be defined before production.

Can magnesium castings be machined?

Yes. Magnesium machines efficiently, making it suitable for precise bores, threads and sealing surfaces. The supplier must use appropriate chip handling and fire-safety controls.

When is magnesium die casting economical?

It becomes attractive when repeat volume spreads tooling cost and the lightweight integrated casting replaces machining or a multi-part assembly. Compare tooling, unit cost, finishing and assembly over the expected program life.

Start a Magnesium Die Casting Project

A successful project connects alloy selection, part design, die construction, casting parameters, finishing and inspection from the beginning. Early DFM reduces tooling changes and improves production stability.

Send your CAD model, drawing, quantities and finish requirements through our request-a-quote page. You can also compare this process with our aluminum casting prototype guide and CNC machining services.