Aluminum pitting corrosion is a localized form of attack that buyers should review against the actual part, finish and exposure. A clean-looking sample photograph cannot establish how a supplied component will perform in a wet or chloride-containing environment.
Start with the application. Identify where water can collect, which surfaces remain exposed and what evidence supports the proposed material and finish. Then give the supplier one written requirement that can be checked on the delivered parts.
On this page
Aluminum pitting corrosion: what buyers need to distinguish
TWI’s overview of corrosion describes pitting as localized damage that forms holes or cavities. It explains that pitting can begin where a protective film or coating breaks down and can be difficult to detect. Small overall material loss can still accompany consequential local damage.
For a buyer, the practical question is whether the proposed evidence evaluates the relevant local damage. A photograph of the overall surface or a single total weight figure may leave that question unanswered.
Do not label every visible mark as a pit. Scratches, staining and coating defects need their own assessment. Keep photographs and observations separate from a confirmed diagnosis in the receiving record.
For related but different mechanisms, see our guides to filiform corrosion under coatings and galvanic corrosion at material contacts. Confirm which mechanism the supplier’s report actually addresses.
1. Describe where the aluminum will be used
The Hydro Solar Design Manual explains the protective role of aluminum’s oxide film and its sensitivity to chloride-containing conditions. It describes pitting initiation at local weaknesses or discontinuities in that protection, including mechanical damage.
Give the supplier a description of the real environment. Separate indoor dry use from outdoor weather exposure, water contact or locations near salt-containing contamination. State whether the part is sheltered, regularly washed or left in a position where liquid can remain.
Describe cleaning products and foreseeable contamination when they are known. If an exposure has not been determined, record that uncertainty in the RFQ. Avoid letting a supplier infer an environment from the product name alone.
Use the same description for every quotation. Otherwise, two offers may appear comparable while their material and finish recommendations assume different conditions.
2. Identify the material and complete surface condition
Hydro’s manual identifies suitable alloy selection and surface treatment as possible measures for reducing pitting risk. These measures still need to be evaluated for the specific application.
Ask the supplier to identify the offered alloy and finish, together with the surfaces included in the finish specification. Keep this information beside the part drawing and order revision.
Describe any cutting, drilling or subsequent assembly steps. Confirm how newly exposed edges and locally disturbed surfaces are addressed in the agreed process. Do not assume a finish designation automatically covers every later operation.
For anodized parts, our anodizing sealing review helps organize questions about the supplied finish. It does not replace application-specific corrosion evidence.
3. Review where the assembly holds water
Hydro’s manual also discusses cleaning, ventilation of tight assemblies and profile arrangements that avoid stagnant water. It notes that pit shapes can vary and that narrow, deeper pits may be difficult to detect.
Review the assembled position rather than the loose profile alone. Identify enclosed spaces, horizontal recesses and interfaces that need attention from the product designer or responsible engineer.
Ask who will review drainage and access for cleaning. Keep any proposed design change subject to the assembly’s functional requirements. A general suggestion to remove water is not approval to change a structural connection or sealed enclosure.
Write down which organization owns this review. The extrusion supplier, finish provider, cutting supplier and final assembler may each control a different part of the outcome.
4. Request evidence that answers the purchasing question
Begin with the acceptance requirement, then ask what evaluation supports it. Request identification of the test specimens, finish condition, exposure method and observed result. The report should explain its scope and limitations.
Use the following review sheet to keep quotations clear. It is a buyer’s information checklist, not a test method or acceptance standard.
| Information requested | Why it helps the review |
|---|---|
| Part and finish identity | Connects the evidence to the configuration being offered. |
| Specimen condition | Shows whether the evaluated surface represents the relevant delivered or assembled condition. |
| Exposure and evaluation | Makes the basis of the reported outcome visible. |
| Acceptance and limitations | Separates the agreed requirement from a broader marketing claim. |
A report on a different finish or a flat reference specimen may be useful background. Ask the responsible reviewer whether it represents the exposed features of your component before accepting it as purchasing evidence.
Read our salt spray testing guide when that method appears in an offer. Keep a laboratory result’s stated scope separate from a claim about service life in the installed environment.
Prepare a clear cutting and receiving handoff
For cut aluminum parts, send the drawing revision, stock identity, finished length requirements and visible-surface handling requirements together. State which finish operations occur before or after cutting.
Ask the cutting supplier how representative pieces will be identified and handled. Keep the agreed dimensional check separate from the corrosion assessment so each result has a clear purpose.
If receiving inspection finds suspicious marks, record the lot identity, location and photographs. Refer diagnosis and acceptance to the responsible material or finish reviewer. Avoid removing the evidence through an improvised repair before that review.
Send JiurunCut your profile drawing and cutting requirements for a discussion of the cutting arrangement. Include the agreed surface-handling requirements so the inquiry describes the component that will actually be processed.
Questions buyers ask
Does aluminum’s oxide film eliminate pitting risk?
No. The relevant review includes the actual exposure, material, finish and local surface condition. General corrosion resistance does not establish approval for every application.
Can a clean sample photo prove resistance?
No. A photo can document visible condition and sample identity. It needs supporting evaluation when the purchasing requirement concerns corrosion performance.
Is pitting the same as filiform corrosion?
No. Keep the mechanism named in the report clear. Our separate filiform guide addresses thread-shaped attack associated with coated surfaces.
Should every quote use the same acceptance requirement?
Yes. Give suppliers one application description and written requirement, then compare how each offer supports that requirement.