As we started producing a large order for a top automotive company, everything seemed to be going smoothly.
However, when the first batch of cast aluminum parts came off the line, we noticed some hairline cracks on their surfaces.
It was a setback, but we knew we had to address the issue quickly and uphold our reputation for excellence.
Cast aluminum parts may crack due to different reasons, such as thermal stress, inadequate cooling, impurities in the alloy, and improper casting techniques. To make high-quality cast aluminum parts meet strict performance requirements, we have to understand and deal with these causes well.
As you read on, you will find the common causes of cracks in cast aluminum parts, the types of cracks you may have, how to fix these problems, and some good practices to prevent them.
Whether you are a buyer, an engineer, or a business owner, this guide shares the knowledge you need to achieve good-quality cast aluminum components.
What Causes Cracks in Cast Aluminum Parts
Thermal Stress
During the casting process, rapid temperature changes and uneven cooling can generate thermal stress, leading to internal stress and potential cracks.
This is particularly severe in large or complex castings with uneven wall thickness, as the cooling and solidification rates vary in different regions.
Controlling the cooling rate and ensuring uniform cooling of the entire casting is crucial for preventing thermal shock, differential shrinkage, and subsequent cracks.
Impurities and Alloy Composition
The presence of impurities or improper alloy composition, such as hydrogen gas or non-metallic inclusions will create weak points, which may develop into cracks under stress.
The impurities could be brought in during the melting process or the raw materials.
Casting Techniques
Deficiencies in casting technology, such as improper mold design, insufficient mold filling, or imperfect gating systems, may lead to defects in cast aluminum.
These defects often become the root cause of cracks.
For example, improper gating may cause hot spots, leading to thermal stress and ultimately cracking.
Crack Types of Cast Aluminum Parts
Hot Cracks
Hot cracks occur at high temperatures, usually during the solidification process.
Hot cracks are usually caused by thermal stress, and improper impurities or alloy composition.
Hot cracks usually form along the weakest grain boundaries of materials, and if not addressed, they can rapidly propagate.
Choosing the right alloy and controlling the cooling rate can help prevent the occurrence of hot cracks.
Cold Cracks
Cold cracks form after the solidification of the parts, usually due to mechanical stress or cooling processes.
They may be caused by residual stresses generated during handling, machining, or casting processes. Cold cracks usually occur in areas with high residual stress, such as sharp corners or parts with different thicknesses.
Heat treatment after casting (such as stress relief) can help reduce the risk of cold cracks.
Shrinkage Cracks
Shrinkage cracks occur during the cooling process and are caused by uneven cooling rates in different areas of the casting.
When certain areas solidify faster than others, differential shrinkage occurs, leading to internal stress.
This type of crack usually occurs in thicker areas of the casting or areas with uneven cooling rates, such as connections, corners, or in castings with complex geometries.
Thermal Fatigue Cracks
Thermal fatigue cracks are generated after repeated heating and cooling cycles.
Over time, the expansion and contraction of materials caused by thermal cycling can lead to fatigue in aluminum structures.
These cracks typically occur in castings with constantly changing temperatures, such as engine components or industrial machinery parts, where thermal stress is a constant factor.
How to Prevent Cast Aluminum Parts from Cracks
Control Cooling Rates
Uniform and controlled cooling can minimize cracks caused by thermal stress.
At CEX Casting, we offer in-house mold design and making services with carefully designed mold cooling channels to ensure uniform temperature distribution.
This can prevent hot spots and drastic temperature changes that will lead to thermal stresses and cracks.
Optimizing Mold Design
CEX Casting offers advanced mold flow analysis services to design the optimal mold and gating system before the actual casting production.
This ensures smooth metal flow and reduces turbulence, thereby minimizing casting defects in subsequent production, such as porosity and inclusions that can lead to cracks.
Use High-Quality Alloys
Selecting the high-purity aluminum alloys and controlling the alloy composition to reduce the impurities, thereby reducing the formation of internal stress and cracks.
At CEX Casting, we procure patented high-purity raw materials and use centralized melting processes to ensure uniform alloy quality and precise temperature management, to produce castings with minimal impurities.
Regular Inspection
Using non-destructive inspection methods to identify internal defects before they develop into cracks.
CEX Casting is equipped with an X-ray machine that performs internal non-destructive inspections of castings to detect and prevent defects as early as possible.
Utilize Squeeze Casting
The high pressure applied during the squeeze casting process helps to close the voids, reduce gas inclusions, and thus make the material structure denser and more uniform.
The decrease in porosity directly reduces the internal stress points that may cause cracks.
In addition, the controlled solidification process can ensure the maximum reduction of thermal gradients, thereby reducing the possibility of thermal stress cracks.
At CEX Casting, we have further optimized the squeeze casting process by utilizing patented squeeze casting equipment that enables us to strictly control every aspect of the process, ensuring that each part meets strict quality standards and is less prone to cracking.
How to Fix Cracked Cast Aluminum Parts
Welding
Tungsten Inert Gas (TIG) welding and Metal Inert Gas (MIG) welding are the most common welding techniques used for repairing cracks in cast aluminum parts.
Both methods provide strong and durable repairs if performed correctly.
Adhesive Bonding
For smaller cracks, high-strength adhesives can be used to bond the crack surface.
This method is less effective for high-stress applications but is suitable for low-stress components.
It is commonly used for temporary repairs or in combination with other repair methods to provide additional support.
Mechanical Fastening
In some cases, mechanical fasteners like screws or bolts can be utilized to clamp the cracked parts.
Mechanical fastening can be a quick and effective solution for non-critical areas, but it may not recover the full strength of the part.
Replacement
If the crack is severe and the part cannot be effectively repaired, especially for critical parts that are crucial for safety and performance, replacement may be the best option.
Ensuring the use of improved technology to cast new parts helps prevent future problems.
At CEX Casting, we utilize an optimized squeeze casting process to produce high-quality, crack-resistant cast aluminum parts.
Conclusion
Understanding the causes of cracks in cast aluminum parts and implementing the best preventive measures is crucial for maintaining product quality and integrity.
By controlling thermal and mechanical stresses, improving casting techniques, using high-quality materials, and employing advanced casting methods such as squeeze casting, the occurrence of cracks in cast aluminum parts can be prevented as much as possible.
At CEX Casting, we are committed to providing virtually defect-free, high-performance aluminum squeeze castings to meet our customers’ strict requirements.
Contact us now to learn how we can help your project achieve outstanding results.