Introduction
Aluminum gravity casting, also called permanent mold casting, remains one of the most reliable manufacturing methods for medium-volume, high-integrity aluminum components. It sits between sand casting and high pressure die casting in both capability and economics, and it is often the best choice when strength, pressure tightness, and tooling payback must all be balanced.
At Bohua Casting, we have produced gravity cast components for more than 20 years for automotive, industrial, and energy customers. As a TS16949-certified manufacturer, we use standardized controls from melt preparation through final inspection, so parts are not only castable, but repeatable in serial production. This guide explains how the process works, where it outperforms alternatives, and how to evaluate it for your next program.
What Is Aluminum Gravity Casting?
Gravity casting is a process in which molten aluminum is poured into a reusable metal mold and fills the cavity under gravity only, without high-pressure injection. The mold is usually steel or cast iron, designed with gating and riser systems to control flow and feed shrinkage during solidification.
Because filling is slower and less turbulent than high pressure die casting, gravity cast parts typically show lower gas entrapment and a denser microstructure. This directly supports:
- •better mechanical properties after heat treatment
- •improved pressure-tight performance
- •lower risk of porosity-related field failures
Gravity casting is commonly selected for structural or semi-structural parts where long-term durability matters more than ultra-fast cycle time.
The 5-Step Aluminum Gravity Casting Process
A stable result depends on disciplined execution at each stage. Below is the workflow we follow in production.
Step 1: Mold Preparation
Permanent mold casting begins with mold readiness. Before pouring, the mold is:
- •cleaned to remove prior-cycle residue
- •coated with a refractory release layer
- •preheated to a controlled temperature window
- •assembled and checked for vent and gating condition
The mold coating serves multiple purposes: it protects tool surfaces, controls local heat transfer, and supports clean release during ejection. Preheating reduces thermal shock and helps the first metal front flow consistently, especially in sections with varying wall thickness.
For new programs, we validate thermal behavior using trial pours and section checks, then lock process parameters into control plans.
Step 2: Pouring
Molten aluminum is transferred from holding furnace to mold using controlled ladling practice. Pouring speed and stream stability are critical. If pouring is too aggressive, turbulence introduces oxide films and gas. If too slow, misruns and cold shuts become more likely.
During this step we control:
- •melt temperature at pour
- •hydrogen and inclusion status from melt treatment
- •ladle cleanliness and transfer time
- •operator method and consistency
For automotive and pressure-tight programs, we use stricter upper and lower limits with documented traceability by heat number.
Step 3: Solidification and Feeding
After filling, the casting solidifies in the metal mold. This stage determines most internal quality outcomes. Proper gating and riser design keep feed paths open long enough to compensate for solidification shrinkage in heavy sections.
Compared with die casting, gravity casting cools more gradually, which helps reduce trapped gas defects and improves metallurgical quality. Chills may be added where directional solidification is needed, and process windows are tuned to keep shrinkage porosity away from critical zones.
At Bohua, first-article validation includes sectioning and radiographic review to confirm that the solidification pattern matches simulation and design intent.
Step 4: Ejection
Once the part reaches safe release temperature, the mold is opened and the casting is removed. Ejection may be manual or assisted depending on part geometry. The goal is to avoid distortion while maintaining cycle time.
Tool maintenance discipline is important here. Sticky release, surface buildup, or ejector wear can quickly create dimensional drift or cosmetic defects. We use preventive maintenance intervals by shot count and keep mold history records for long-run stability.
Step 5: Finishing and Secondary Operations
After removal, gates and risers are trimmed. Depending on specification, parts then move through:
- •shot blasting or surface cleaning
- •heat treatment (for alloys like A356)
- •CNC machining of functional features
- •leak testing, dimensional inspection, and final visual standards
This step is where casting quality is converted into final product capability. A good casting process without controlled machining and inspection still creates risk. That is why integrated casting plus machining under one quality system is preferred for B2B buyers.
Typical Alloys for Gravity Casting: A356 and ZL114
Alloy selection should follow end-use requirements, not habit. Two alloys frequently specified in gravity casting programs are A356 and ZL114.
A356
A356 is one of the most common gravity casting alloys for structural and pressure-related parts. It offers:
- •strong strength-to-weight performance
- •good corrosion resistance
- •good castability for medium-complex geometries
- •effective response to T6 heat treatment
Because A356 can be heat treated, it is widely used where mechanical performance must be raised beyond as-cast condition.
ZL114
ZL114 is often selected for applications requiring robust mechanical behavior with stable casting performance in permanent molds. It is used across automotive and industrial components where reliability under load is essential.
Alloy Comparison Overview
| Factor | A356 | ZL114 |
|---|---|---|
| Typical use focus | Structural and pressure-tight parts | Durable structural and industrial components |
| Heat treatment compatibility | Excellent (commonly T6) | Commonly used with controlled thermal processing |
| Corrosion behavior | Strong | Strong |
| Casting behavior in gravity mold | Stable with proper gating and melt control | Stable for robust sections and demanding service |
| Common industries | Automotive, pump/valve, energy | Automotive, machinery, industrial systems |
Final selection should always be validated by mechanical targets, service environment, machining strategy, and cost model.
Gravity Casting Advantages vs Die Casting
A frequent sourcing mistake is choosing process by headline unit price only. Real cost and risk depend on performance targets, defect sensitivity, and lifecycle requirements.
Practical Comparison
| Decision Factor | Gravity Casting | High Pressure Die Casting |
|---|---|---|
| Filling method | Gravity-fed, low turbulence | High-speed injected under pressure |
| Tooling investment | Lower to medium | High |
| Typical annual volume sweet spot | Medium volume | High to very high volume |
| Wall thickness capability | Better for medium-thick sections | Better for thin walls |
| Internal porosity risk | Lower with correct melt and feed control | Higher gas entrapment risk |
| Heat treatment suitability | Strong option for heat-treatable alloys | Often limited by porosity behavior |
| Mechanical property potential | High, especially after heat treatment | Good, but process-limited for some structural needs |
| Typical use case | Structural, pressure-tight, durability-focused parts | Complex thin-wall parts at large volume |
Where Gravity Casting Wins
- •parts needing higher integrity and lower porosity
- •components that must pass pressure or fatigue-related criteria
- •programs where tooling budget must stay controlled
- •projects requiring heat treatment to meet strength targets
Where Die Casting Wins
- •very high annual output
- •thin-wall, highly detailed geometry
- •near-net shape and fast cycle requirements
For many OEMs, both processes are used in the same product family. The right decision is part-specific, not company-specific.
Industry Applications
Automotive
Automotive customers use gravity casting for brackets, housings, suspension-related components, and other parts where durability and safety margins are important. These parts often require controlled mechanical properties and documented process traceability. With TS16949 controls, gravity casting supports PPAP-style quality requirements and stable serial production.
Industrial Equipment
Industrial programs value uptime and service life. Gravity casting is commonly used for pump bodies, valve components, gearbox housings, and machine structure elements that see cyclic loading or fluid pressure. Better integrity in thicker sections can reduce leak and crack risk over long service intervals.
Energy and Power Systems
In energy applications such as compressor bodies, inverter-related housings, and power equipment components, thermal cycling and reliability are major concerns. Gravity cast aluminum parts provide a practical balance of mechanical performance, corrosion resistance, and manufacturability for these environments.
Quality Control Framework for Gravity Casting
Stable quality is built before final inspection. At Bohua, our control strategy combines process discipline with targeted verification tools.
1) Chemical Composition Control with Spectrometer
Every melt must meet alloy chemistry limits. Optical emission spectrometer checks verify composition before production pouring and during heat management windows. This avoids property drift caused by uncontrolled chemistry.
2) Internal Defect Detection with X-ray
Radiographic inspection is used for first article and critical serial parts to detect shrinkage porosity, inclusions, and internal discontinuities. For pressure-related programs, X-ray acceptance criteria are linked to functional risk zones defined during APQP planning.
3) Dimensional Verification with CMM
Coordinate measuring machine inspections confirm critical dimensions, datums, and geometric relationships. This is essential when cast features interface with machined assemblies. We combine CMM checks with in-process gauging to prevent drift across long runs.
4) Process Documentation and Traceability
Inspection only finds defects after cost is already added. Prevention requires control plans, work instructions, and parameter records for mold temperature, melt temperature, pouring practice, and cycle timing. Each batch is traceable to material and process records for containment speed if issues occur.
5) Integrated Casting + Machining Quality Loop
When casting and machining are controlled together, geometric capability and scrap rates improve. Feedback from machining can identify recurring cast variation early, allowing tool or process correction before quality escapes.
Implementation Checklist for Buyers
If you are evaluating aluminum gravity casting for a new part, use this practical checklist:
- •define mechanical and leak-tight requirements first
- •confirm whether heat treatment is required
- •review wall thickness distribution and feeding risk zones
- •align alloy choice (A356, ZL114, or alternative) with service conditions
- •set inspection plan: spectrometer, X-ray, CMM, plus functional tests
- •estimate annual demand to validate process economics vs die casting
- •request a DFM review before tool release
This upfront work shortens launch time and reduces engineering changes after tooling.
Why Global B2B Buyers Work with Bohua
Bohua has over 20 years of aluminum casting experience across gravity casting, die casting, low pressure casting, and sand casting. For gravity casting projects, customers rely on us for:
- •TS16949-certified quality management
- •proven alloy capability including A356 and ZL114
- •in-house QC tools including spectrometer, X-ray, and CMM
- •process engineering support from DFM through mass production
- •integrated machining and final inspection under one system
Our role is not only to produce castings, but to help customers choose the right process for performance, cost, and lifecycle risk.
Conclusion
Aluminum gravity casting is a high-value process for medium-volume components that demand reliability, mechanical performance, and controlled porosity. When mold design, melt practice, and quality controls are executed correctly, it delivers durable parts across automotive, industrial, and energy applications.
If your team is deciding between gravity casting and other aluminum processes, we can help you evaluate geometry, alloy, and production targets with a manufacturing-first perspective.
Contact Bohua to request a technical review, process recommendation, and quote for your gravity casting project.
Related Resources
- •A356 Aluminum Alloy Data Sheet �?Review the most common gravity casting alloy for structural parts
- •Aluminum Gravity Casting Process �?See how permanent mold casting works in production
- •Gravity Casting vs Die Casting �?Compare process trade-offs before sourcing