CNC machined parts often get exposed to moisture, chemicals or tough environments. Corrosion resistance is how well these parts withstand such conditions. Ignoring corrosion resistance during design or manufacturing can lead to part failure, wasted time and higher costs.
In this blog post we will show you the clear steps to test, assess and strengthen the corrosion resistance of CNC parts.
Testing Methods for Corrosion Resistance Evaluation in CNC Parts
CNC machined parts must withstand their working conditions. To assure this you need to check their corrosion resistance early by using reliable testing methods in both laboratory and quality control.
1. Salt Spray (Fog) Test (ASTM B117 / ISO 9227)
In the salt spray test, CNC parts go into a sealed chamber filled with a fine mist of 5% sodium chloride at 35°C. This simulates salty harsh environments and quickly checks if part’s protective coating works well. For example zinc plating should last at least 96 hours while nickel‐zinc coatings can last up to 720 hours. This longer resistance to corrosion means better protection for the part.
2. Immersion Testing
Immersion testing evaluates corrosion by putting CNC parts directly into corrosive liquids. Testers use 3 to 5% salt water, alkaline or acidic solutions and submerge the parts for 24 hours to several weeks. After exposure they measure both weight loss and visible surface damage.
These results help calculate corrosion rates in mm/year. Because results can show up in 24 hours therefore immersion testing is a quicker initial test as compared to salt spray testing.
3. Cyclic Corrosion Testing (CCT)
Cyclic corrosion testing adds cycles of salt spray, drying and humidity instead of using only constant salt fog. This simulates real world weather changes. Each cycle normally takes 24 hours and some tests run for several weeks. This shows how CNC parts react to changing moisture and temperature; and this gives more accurate durability results.
4. Mixed Flowing Gas (MFG) Testing
MFG testing simulates the effects of atmospheric pollution on sensitive metals and electronic parts. In this method CNC parts are exposed to a controlled mixture of gases—chlorine, hydrogen sulfide, nitrogen dioxide and sulfur dioxide—at parts‐per‐billion levels.
Test chambers are set at 30°C and 70% humidity for 10 to 21 days. This accelerates corrosion and simulates 10 to 20 years of real world exposure in about 2 weeks. Therefore defense and aerospace industrial fields use MFG testing for parts that must withstand tough environments.
5. Electrochemical Methods (e.g., Polarization, Electrochemical Impedance Spectroscopy)
Electrochemical methods give us insight into both corrosion rates and coating effectiveness. Different techniques like potentiodynamic polarization and electrochemical impedance spectroscopy measure corrosion resistance and current in real time.
Labs normally set up a three electrode cell with a salt solution and can mostly detect corrosion in just an hour. This allows for material comparisons and helps in selecting the best CNC finishing options.
At RICHCONN, we make corrosion testing a standard part of our process. Our team runs cyclic corrosion, salt spray and electrochemical tests according to ISO and ASTM standards. This assures your CNC parts meet the durability requirements.
6. Electropolishing and Surface Profilometry
Electropolishing improves corrosion resistance by making the surface very smooth. This process uses electrochemistry to strip away microscopic layers from CNC parts. It removes small cracks and flaws that can lead to corrosion. After electropolishing, surface profilometry checks the new smoothness. High resolution scans verify that the pits are gone; which means CNC parts last longer and perform better.
7. Hardness Testing (Vickers, Rockwell)
Hardness testing verifies that CNC parts meet strength requirements. Vickers or Rockwell test uses an indenter to press into the material’s surface. The result is a hardness value such as HV or HRC. Surfaces with higher hardness resist wear and some forms of corrosion better. Therefore regular hardness testing is important for quality control and to approve finished parts.
8. Microscopic and Visual Inspection
Visual inspection can show discoloration or rust on a CNC part. But most problems start at a microscopic level. Inspectors use microscopes to find early signs of pitting, microcracks or crevice corrosion. Finding these flaws early is key to preventing failures in the future.
Comprehensive Table for Testing Methods Overview
| Test Method | Type | Standard / Protocol | What It Measures | Typical Outcome / Interpretation |
|---|---|---|---|---|
| Salt Spray Test | Lab Simulation | ASTM B117 / ISO 9227 | Time to visible rust or pitting in a saline mist | 96 h (zinc) to 720 h+ (Ni‐Zn); higher = better resistance |
| Cyclic Corrosion Test (CCT) | Lab Simulation | Varies by ISO or OEM | Performance over humidity, salt, dry cycles | Mimics real world; useful for outdoor durability validation |
| Immersion Test | Lab Simulation | ASTM G31 / G1 | Surface changes or weight loss after soaking in corrosive fluids | Measures metal loss over time; best for chemical resistance tests |
| Mixed Flowing Gas (MFG) Test | Lab Simulation | ASTM B845 / IPC-TM-650 | Corrosion under polluted air (Cl₂, NO₂, SO₂, H₂S) | Well known in electronics; checks sensitivity to environmental gases |
| Electrochemical Impedance / Polarization | Electrochemical Lab Method | ASTM G5 / G59 / G106 | Corrosion rate, current flow, protective film breakdown | Useful for advanced coating performance & lifespan analysis |
| Electropolishing & Surface Profilometry | Surface Inspection | ISO 4287 / ASME B46.1 | Surface roughness (Ra, Rz), profile uniformity, crack removal | Smoother surfaces = less corrosion prone; mostly <0.2 µm Ra |
| Hardness Testing | Mechanical Inspection | ASTM E18 (Rockwell), E384 (Vickers) | Substrate hardness & its effect on coating adhesion/ resistance | Assures durability under stress; too soft = coating damage risk |
| Microscopic / Visual Inspection | Physical Inspection | ISO 6507 / ISO 10289 | Surface flaws, pitting, SCC, crevice corrosion | Detects early corrosion; paired with magnification & cross sections |
If you are unsure which test matches your needs, RICHCONN’s engineers can assist you in choosing the best evaluation method for your next part.
Corrosion Resistance Factors
Knowing what affects a part’s corrosion resistance is key to choosing the right materials and designing durable parts. Here are the main factors that impact corrosion resistance in CNC parts and how to improve protection at each stage.
Material Selection and Alloy Composition
Choice of right material is a very important step in preventing corrosion. Aluminum, titanium and stainless steel each offer different levels of protection. The specific alloy you use matters too. For example 316L stainless steel has molybdenum which makes it highly resistant in marine environments.
Choosing the wrong alloy can cause fast pitting. Moreover using different metals together can also cause galvanic corrosion. To prevent this, choose those alloys which match the environment and use insulators to keep dissimilar metals apart.
Surface Finish and Machining Quality
Surface quality of a part also has a direct impact on its corrosion resistance. Machining can leave rough surfaces with microcracks and small grooves. These imperfections trap moisture and contaminants. As a result pitting and rust can start more easily. Smoother surfaces give corrosive agents fewer places to attack.
To improve protection apply post processing methods like mechanical polishing or electropolishing. These treatments smooth out the surface, remove flaws and increase the parts’ durability.
Post Processing Treatments
Surfaces left unprotected after machining are at high risk of corrosion. Heat affected zones from machining can further reduce corrosion resistance. The best way to address these issues is to apply protective finishes. For aluminum, anodizing forms a hard oxide layer that shields the surface.
Stainless steel benefits from passivation which removes contaminants and creates a protective film. Other reliable methods are powder coating and electroplating with metals like nickel or zinc. These coatings protect the part from environmental exposure.
Design and Geometry Considerations
Physical design of a part has a big role in its corrosion resistance. Sharp corners, tight crevices and blind holes collect contaminants and moisture. When moisture gets trapped, corrosion can start and spread quickly. Complicated shapes can also stop proper drainage and let corrosive substances gather on the surface.
Making simple changes like rounding corners or adding fillets helps improve airflow and drainage. In assemblies, placing sealants or gaskets at interfaces between parts can block corrosive agents from reaching those areas.
Operational Environment
Corrosion risk is environment dependent as well. Acidic vapors, high humidity and saltwater speed up metal degradation. Corrosion rates double with every 10°C increase in temperature. Marine or outdoor environments expose parts to aggressive agents like chloride ions which can cause pitting in stainless steel.
To reduce these risks store parts in controlled environments and use corrosion inhibiting oils during shipping. For parts that must operate in harsh environments, use coatings designed for those environments like marine grade epoxy or Type III hard coat anodizing.
General Prevention and Maintenance Strategies
A maintenance plan along with good design and material choice is your best defense against corrosion over time.
Schedule regular inspections
Inspect in‐service parts regularly to find early signs of corrosion like rust or pitting. Early detection means timely repairs and avoidance of expensive failures. A simple plan with annual inspections and daily visual checks is enough.
Train staff for proper handling
The working team’s actions matter. Teach staff how to handle and clean parts. This prevents contamination or scratches that can start corrosion.
Plan for re‐passivation or re‐coating
Coatings and passivation layers wear down, particularly in harsh conditions. To keep parts protected for the long term, plan re‐coating or re‐passivation.
Use QA tools to check production
Always check that coatings meet quality standards. Use devices like coating thickness meters to assure coatings reach the required micrometer thickness for proper protection.
At RICHCONN, we use these QA tools too, so that you know every batch meets your finish and durability needs.
To Sum Up
Checking corrosion resistance of CNC parts is crucial for reliable long life in many industrial fields. You can make components last longer if you choose the right materials, apply the right surface finishes and use strict testing procedures.
If you want CNC machined parts that strongly resist corrosion then contact Richconn. Our quality control is very strict; therefore you will always get durable CNC parts.
Related Questions
Smaller surface roughness (Ra) values at or below 1.6 μm help prevent corrosion. Fewer rough spots mean fewer places for corrosive substances to collect.
There are several types. Uniform corrosion spreads across the whole surface. Localized corrosion like crevice and pitting corrosion targets particular spots on the metal.
Corrosion resistance in CNC parts depends on many factors. The surface finish quality, material used (like stainless steel, titanium or aluminum alloys), any coatings for protection and treatments like anodizing; all have a role.
Yes pH of a solution has a big impact on corrosion. Metals corrode faster in environments that are very acidic (pH below 4) or very alkaline (pH above 10).
