Overview
ISO 11846:1995 is an internationally recognized standard titled "Corrosion of metals and alloys - Determination of resistance to intergranular corrosion of solution heat-treatable aluminium alloys." Developed by the International Organization for Standardization (ISO), this standard specifies test methods for evaluating the susceptibility of solution heat-treatable aluminium alloys to intergranular corrosion. It applies to cast and wrought aluminium alloys in various forms, including castings, forgings, plates, sheets, extrusions, and semi-finished or finished parts without protective coatings.
The standard enables manufacturers, quality control professionals, and material engineers to perform comparative assessments of aluminium alloys by their corrosion resistance depending on factors like chemical composition, manufacturing methods, and heat treatment processes. Its goal is to provide reliable, standardized test procedures to help improve product durability and performance in environments where corrosion resistance is critical.
Key Topics
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Scope and Applicability
ISO 11846 covers solution heat-treatable aluminium alloys that have undergone thermal processing, in their natural or artificially aged states. It excludes alloys with protective coatings and targets relevant industry sectors dealing with structural and engineering aluminium products.
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Test Specimens and Preparation
Specimens may be taken from critical areas of the product that reflect minimum cooling rates during quenching-typically prone to corrosion. The standard details sampling strategies for various forms such as thin sheets, forgings, extrusions, and small parts quenched in baskets or on racks to ensure representative test results.
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Surface Preparation and Degreasing
Prior to testing, specimens must be degreased with organic solvents and are prepared either mechanically or chemically. For clad aluminium products, the cladding layer is carefully removed to expose the heat-treatable base material for accurate testing.
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Testing Procedures
ISO 11846 outlines three main testing methods:
- Method A: Assessment of quenching quality via immersion in sodium chloride and hydrogen peroxide solution for 6 hours.
- Method B: Comparative determination of intergranular corrosion resistance in sodium chloride-hydrochloric acid solution over 24 hours.
- Method C: Electrochemical anodic polarization to estimate susceptibility, particularly useful for aluminium-lithium alloys, involving potential-controlled exposure in sodium chloride solution.
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Metallographic Examination
After exposure, specimens are metallographically analyzed to evaluate corrosion attack depth and extent, primarily at grain boundaries. Microscopic inspection is performed at magnifications of 100x to 500x to confirm intergranular corrosion presence.
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Interpretation and Reporting
Acceptance criteria are determined based on the extent and severity of intergranular corrosion, with results expressed as percentages and corrosion ratings. Test reports include detailed alloy specifications, manufacturing and heat treatment data, specimen conditions, test procedures used, and exposure durations.
Applications
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Material Quality Control
ISO 11846 offers manufacturers and suppliers a well-defined protocol to assess and control the heat treatment quality and corrosion resistance of aluminium alloys used in aerospace, automotive, marine, and construction industries.
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Alloy Development and Selection
Researchers and engineers utilize this standard to compare the intergranular corrosion resistance of different aluminium grades, facilitating informed material selection tailored to specific environmental exposures.
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Supplier-User Agreements
The standard provides a common ground for defining corrosion resistance criteria between suppliers and users, ensuring consistent quality and performance verification of heat-treatable aluminium components.
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Corrosion Testing Laboratories
Independent labs employ the standardized methods for reliable and reproducible testing to support certification, compliance, and failure analysis.
Related Standards
- ISO 3696:1987 – Water for Analytical Laboratory Use: Specification and test methods, used for preparing testing solutions.
- ISO 8044:1989 – Corrosion of Metals and Alloys: Vocabulary, defining key terms used in corrosion testing.
- ISO 8407:1991 – Removal of Corrosion Products from Corrosion Test Specimens, detailing cleaning procedures post-testing.
- ASTM G110-92 – Practice for Evaluating Intergranular Corrosion Resistance of Heat-Treatable Aluminium Alloys by Immersion.
- GOST 9.021-88 – Russian Standard for Accelerated Intergranular Corrosion Testing of Aluminium Alloys.
These related standards complement ISO 11846 by covering vocabulary, solution preparation, specimen cleaning, and additional corrosion testing practices.
Keywords: ISO 11846, intergranular corrosion, aluminium alloys corrosion resistance, solution heat-treatable aluminium, corrosion testing methods, metallographic examination, alloy quality control, heat treatment assessment, corrosion standards, aluminium corrosion testing.
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