13 Types of Aluminum Casting Defects and How to Prevent Them

When I saw the molten aluminum flowing smoothly into the mold, I recalled a critical moment in our company’s history.

We once suffered a significant production setback due to unexpected casting defects.

This challenge not only tested our resilience but also inspired our determination to master the secrets of aluminum casting, leading us to adopt advanced techniques and rigorous quality controls to guarantee accuracy and reliability in our processes.

Defects of aluminum casting can impact the quality and performance of the final products. Here are 13 common defects and prevention methods: Porosity, Cold Shuts, Misruns, Shrinkage, Inclusions, Hot Tears, Surface Cracks, Flash, Soldering, Blistering, Sand Holes, Scabbing, and Burn-On. Proper mold design and advanced techniques are important to understand and solve these defects through an optimized casting process to make aluminum castings without defects.

By understanding these common defects and applying specific prevention methods, we can greatly improve the quality and reliability of the castings.

Let’s go through each defect and find out how to prevent them effectively.

Common Types of Aluminum Casting Defects

Porosity

Porosity is the formation of small holes inside the castings.

It is usually caused by gas trapped in the casting during solidification.

The main sources of trapped gas include moisture in the mold material, insufficient degassing of the molten metal, and poor venting in the mold.

porosity

Cold Shuts

Cold shuts are the defects that two streams of metal flow together but do not fuse well, which leads to weak spots.

This defect is caused by improper temperature control, slow pouring speed, or turbulence in the mold that disturbs the metal flow.

Misruns

Misruns occur when the molten metal solidifies before filling the mold cavity, resulting in incomplete castings.

The causes of this defect include insufficient pouring temperature, slow pouring speed, or a mold design that is too complex or restrictive for the molten metal to flow freely.

misruns

Shrinkage

Shrinkage defects are the cavities or voids inside the castings, which are caused by the volume reduction during the metal cooling and solidification.

This defect usually happens in the thick sections of the castings, where the metal cools unevenly and forms internal cavities.

shrinkage

Inclusions

Inclusions are the foreign materials in the castings, such as slag, oxides, or sand, which are trapped inside.

The sources of inclusions are dirty or poorly maintained molds, inadequate filtering of the molten metal, or the low quality of raw materials.

sand inclusion

Hot Tears

Hot tears are the cracks that appear during the cooling and contraction of the castings.

They usually happen in areas with high thermal gradients or where the mold design restricts the metal from contracting freely. Inappropriate alloy selection may also cause this defect.

hot tears

Surface Cracks

Surface cracks are the fractures on the surface of the castings.

They are caused by rapid cooling, thermal shock, excessive handling, or stress concentration in the mold.

Inconsistent cooling rates and poor mold design are the main reasons.

surface cracks

Flash

Flash is the extra material that flows out between the mold halves, which creates thin and unwanted projections on the castings.

It is caused by the improper clamping of the mold, excessive pouring pressure, or the misalignment of the mold halves.

flash

Soldering

Soldering is when the molten metal sticks to the mold surface, which leads to surface defects.

It is usually caused by insufficient mold lubrication, incorrect mold material, or overheating of the mold surface.

soldering

Blistering

Blistering is the raised area on the surface of the castings, which is caused by the gas trapped inside expanding during solidification.

This defect is often caused by inadequate venting, excessive moisture in the mold, or high pouring temperatures that lead to gas entrapment.

blistering

Sand Holes

Sand holes are the cavities or depressions on the surface of the castings, which are caused by loose sand particles in the mold.

The poor sand quality, improper sand compaction, and inadequate mold preparation are the main reasons for this defect.

sand hole

Scabbing

Scabbing is the flaking or peeling of the casting surface, which is caused by poor sand compaction, excessive moisture in the sand mold, or improper mold coating.

This defect can weaken the castings and affect the appearance.

scabbing

Burn-On

Burn-on defects are the places where the sand mold fuses with the castings, which leads to rough and uneven surfaces.

This defect is caused by excessive mold temperature, long-time contact between the mold and molten metal, and inadequate mold coatings.

burn-on

How to Prevent Aluminum Casting Defects

Process Optimization

At CEX Casting, we optimize pouring process parameters including pouring temperature, pouring rate, inlet design, and mold design to maintain a steady, continuous flow of molten metal and avoid turbulence to prevent cold shuts, misruns, and inclusions.

In addition, we offer mold flow analysis services that use computer simulations to predict possible defects during the casting process and optimize the process before actual casting, thus minimizing the risk of defects.

模流分析-压缩

Proper Mold Design and Maintenance

To prevent common casting defects, it is important to make sure that the molds are properly designed and maintained.

This includes using the right materials, ensuring proper ventilation, keeping the molds clean and well-lubricated, and avoiding sharp corners or complicated paths that can disrupt metal flow.

At CEX Casting, we offer in-house mold design and making services, eliminating the middleman and ensuring quality molds.

In addition, we regularly provide our customers with free mold maintenance and renewal services to ensure that the molds are always in good working condition.

Learn more about our in-house mold capability.

in-house molding

Advanced Casting Techniques

Advanced casting techniques such as squeeze casting are used to minimize casting defects.

Squeeze casting applies pressure during solidification, which helps to eliminate gas inclusions and shrinkage.

CEX Casting has further optimized the squeeze casting process with patented squeeze casting equipment, resulting in castings that are virtually free of defects and come with excellent mechanical properties.

squeeze casting equipment

Alloy Selection and Treatment

Selection of suitable alloy compositions with appropriate treatments such as degassing and filtration to prevent casting defects.

Using alloys with low gas absorption and good thermal properties to minimize porosity and thermal cracking.

At CEX Casting, we select premium patented alloys and treat them thoroughly to ensure that the final product meets stringent quality standards.

Our commonly used squeeze casting aluminum alloys include A356, A356.2, A380, A319, A319S, AlSi10Mg, and AlSi9Cu3.

Chart: Casting Methods and Their Defects

Defect

Die Casting Squeeze Casting Gravity Casting Sand Casting Permanent Mold Casting

Porosity

x   x x  

Cold Shuts

x   x x

x

Misruns

    x x

Shrinkage

    x  

x

Inclusions

  x x x

 

Hot Tears

        x
Surface Cracks   x x  

x

Flash

x        

Soldering

x        

Blistering

x        
Sand Holes     x x

 

Scabbing       x

 

Burn-On

    x x

x

Squeeze casting is the best choice amongst the various aluminum casting methods as it comes with minimal casting defects, mainly surface cracks and inclusions (if not managed properly).

At CEX, our squeeze casting process minimizes porosities, shrinkages, and other common defects, ensuring the production of high-quality aluminum castings with dense internal structure, smooth surfaces, and excellent mechanical properties.

Defect Free Aluminum Squeeze Castings

At CEX Casting, the internal structure of our aluminum squeeze casting parts can achieve virtually no porosity.

It can avoid defects in traditional aluminum casting methods such as shrinkages, cracks, and other common defects.

The following figures show the near-zero porosity internal structure detected by our X-ray machine, as well as a cross-sectional view of our squeeze casting part showing the flawless internal structure.

X光照片

零件剖面图

How to Check Casting Defects

Establishing strict quality control systems and conducting regular inspections are necessary to find and solve the defects in the early stage of the casting process.

At CEX Casting, we follow ISO 9001 and IATF16949 quality control systems to manage production with high-quality standards.

Moreover, we have introduced a range of quality control equipment, including CMM and X-ray machines, to conduct dimensional inspection and internal non-destructive testing of castings to detect and prevent defects as early as possible.

Learn more about our quality control.

Visual Inspection

Visual inspection is the first and the most direct method to detect surface defects in castings.

At CEX Casting, our trained inspectors examine the castings under adequate lighting to identify visible defects such as surface cracks, porosity, cold shuts, misruns, and surface roughness.

Dimensional Inspection

Dimensional inspection is to measure the physical dimensions of the castings to make sure that they meet the specified tolerances.

At CEX Casting, we conduct dimensional inspection by using calipers, micrometers, coordinate measuring machines (CMM), and other precision measuring tools.

Any deviation from the specified dimensions can indicate defects such as shrinkage or warping.

CMM

Non-Destructive Testing (NDT)

Non-destructive testing (NDT) methods can detect internal and surface defects without damaging the casting.

Common NDT methods include X-ray Radiography, Ultrasonic Testing, Magnetic Particle Testing, and Dye Penetrant Testing.

At CEX Casting, we have introduced an X-ray machine to inspect the internal structure of castings.

X-ray Radiography: a method using X-ray to penetrate the casting and form the image on a radiographic film or digital detector.

It is effective in finding out the internal defects, like porosity, inclusion, and shrinkage.

X光机

Ultrasonic Testing: ultrasonic waves are transmitted through the casting and the change of wave behavior (reflection, refraction) is analyzed to detect the internal defects.

It is especially useful for finding cracks and inclusions.

Magnetic Particle Testing: this method is used for ferromagnetic materials.

A magnetic field is applied to the casting, and iron particles are spread over the surface.

The particles gather at locations with magnetic flux leakage, showing surface and near-surface defects like cracks.

Dye Penetrant Testing: a dye penetrant is applied to the surface of the casting.

After a certain dwell time, the excess dye is removed and a developer is applied.

The developer will draw out the dye from any surface defects, making them visible under UV light or natural light.

Leakage Testing

Leakage testing is used to inspect castings that work under pressure, such as pipes, valves, and engine components.

By applying the internal pressure to the casting to detect if there is any leakage and verify its integrity.

Leakage testing is used to detect defects such as internal porosity and incomplete fusion.

At CEX Casting, we offer two leakage testing methods to our customers, including water immersion testing and helium leakage testing. Learn more.

Conclusion

Understanding and preventing the defects in aluminum casting is crucial for producing high-quality and reliable products.

By using the combination of a robust quality control system, process optimization, the proper mold design, the advanced casting technique, and careful alloy selection, we can greatly reduce the occurrence of casting defects.

Especially squeeze casting, is an effective method to minimize a wide range of defects, ensuring dense and high-integrity castings.

At CEX Casting, we combine these comprehensive strategies into our production, using our patented squeeze casting technique, providing virtually defect-free aluminum castings.

Our commitment to excellence ensures our customers receive the products with the highest standards of quality and performance.

Contact us for more information about our aluminum casting service or to discuss your project requirements.

Let’s work together to achieve flawless aluminum castings for your applications.

 

 

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