Aluminum die casting is widely popular across many industries due to its superior mechanical properties. They offer impeccable quality, performance, durability, and strength-to-weight ratio. All modern die casts require a specific surface finish, coating, polish, or paint for precise outcomes.
They don’t necessarily serve aesthetics as the primary purpose in most die-cast products. And aluminum casts often require this treatment to enhance certain applications’ properties. Various surface finishing can be given to enhance the properties of aluminum castings.
Advantages of Surface Finishing
Providing a functional surface finishing to aluminum castings can provide multitudes of benefits including,
· Corrosion Resistance
Al casts possess excellent corrosion resistance. But this property doesn’t come in handy in aqueous or wet conditions. A good aluminum surface finish can improve corrosion resistance due to minimal roughness.
· Tensile Strength
Sometimes, durability alone can’t meet the product or functionality requirements. A proper finishing method like electroplating can improve the strength. Plating a stronger material to coat the aluminum can impart further tensile tolerance.
· Chemical Inertness
Aluminum surface roughness isn’t inert to certain chemical compounds in specific conditions. A smooth surface can keep the entire exterior intact against chemical attacks. Therefore, die casts become well-suited to challenging atmospheres.
· Pleasant Appearance
Any castings exposed to human eyes will appear poorly due to rough surfaces. But surface finishing imparts smoothness, shiny, and straight aesthetics. This is particularly important for parts used in ornamental or decorative applications.
Common Surface Finishes for Aluminum Castings
Die-casting manufacturers utilize surface finishing techniques according to the material specifications. The most beneficial strategies per the aluminum die casting surface finishing guide are –
Anodizing
This electrochemical process suits common non-ferrous die-cast metals like aluminum, zinc, and magnesium. It offers resistance to scratches and corrosion. There are three types of anodized aluminum finish:
Type I –This type utilize chromic acid to create the thinnest anodized oxide coating (minimum 0.0001″). This makes die casts slightly dyeable with high corrosion resistance.
Type II –It involves sulfuric acid to generate a thicker oxide coating (0.0001″ to 0.002″). Die casts are highly dyeable with excellent corrosion resistance.
Type III –It also uses sulfuric acid like Type II but with an additional high electric current. Thick (more than 0.001″) oxide layers lead to resistance against corrosion and abrasion.
Electroplating
This protective finishing method is almost universal for die cast aluminum surface finish. Passing the cast through an electrolytic setup forms a thin film of other metals on the surface. The part is submerged in a dissolved solution of metal ions for aluminum casts.
Cadmium and zinc are popular for most Al die-cast parts. But other metals are also necessary for well-defined specifications. Improvements in functionality and aesthetics make this technique usable on many complex, large-sized, and customized aluminum products.
Polishing
This process is mostly manual, requiring an abrasive material for the lustering and shiny outcome. Multiple polishing options and methods are available to create the mirror-bright appeal. It involves subsequent roughing, polishing, brightening, and protection of surfaces.
Powder Coating
The application of dry powder is a popular strategy for commercial aluminum products. Proper preparation is necessary to make the powder stick to the surface. Spray guns coat the powder, and heat is applied to cure the combination for a permanent effect.
The powder is either thermoplastic or thermoset plastic to create a flexible finish. Thermoplastic powder is soft and reversible without chemical bonds, making the coat reusable. But thermoset powder creates an irreversible chemical bond upon heating.
Chrome Plating
This process uses the identical electrolytic setup as electroplating. But it specifically requires chromium in the solution for aluminum casting surface finish. A thick hard plating pushes the functionality, whereas a thin decorative plating provides reflective properties.
Anodizing aluminum is one of the best solutions for die castings finish due to abrasion resistance. It gives surfaces a deep, rich, attractive metallic appearance without peeling off. Other options are also preferable based on factors like cost, ease of operation, purposes, etc.
Categories of Die Casting Surface Finish
Manufacturers may categorize the surface finish for aluminum casting in either of the following grades –
- Utility Grade:
A protective coating comes without any cosmetic finish for hidden/non-visible surfaces. It barely concerns surface imperfections.
- Functional Grade:
The finish may feature a decorative coating. And spot-polish or simple painting often patches surface imperfections.
- Commercial Grade:
It concerns good aesthetics, removal of imperfections, and protection. This grade is mostly used in high-stressed structural projects.
- Consumer Grade:
The finishing primarily focuses on decorative properties. Its coating must exhibit minimal surface imperfections.
- Superior Grade:
It entails the application of alloy-dependent coatings to limited regions. The maximum value is in inches, being suitable for smaller areas.
General Process of Aluminum Die Casting Finish
Our aluminum die cast surface finishing guide also provides a generalized phasing of the process –
Phase #01: Deburring
The first stage concerns the removal of unwanted roughness on surfaces. It may include burrs, flashes, sharp edges, and debris. This phase makes the surface shiny, clean, and bright.
Phase #02: Conversion Function Coating
Next, a conversion coating is directly applied to the surface. It removes all the sticky contaminants like oils and agents. Also, the phase prepares surfaces for painting or polishing.
Phase #03: Final Finish
A few casts don’t need this step. This is where one of the mechanical methods implies the surface finish. The method is chosen based on the required properties for improvement.
Sunrise Metal promises to meet your requirements for aluminum die casting from every crucial aspect. Our expert team of professionals is ready to deliver the best surface finishing for your products. Contact us anytime to specify your requirements for surface finish for aluminum casting.