ISO/DIS 22230:2026(en)

ISO/TC 79/SC 5

Secretariat: SAC

Date: 2025-12-22

Specification for phosphate conversion coating on magnesium and its alloys

© ISO 2026

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Contents

Foreword iv

Introduction v

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Information to be supplied by the purchaser 1

5 Requirements 2

5.1 General 2

5.2 Classification 2

5.3 Marking 3

6 Performance requirements 3

6.1 Appearance 3

6.2 Corrosion resistance 3

6.3 Post treatments 3

Foreword

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This document was prepared by Technical Committee ISO/TC 79, Light metals and their alloys, Subcommittee SC 5, Magnesium and alloys of cast or wrought magnesium.

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Introduction

Phosphate conversion coatings are applied to magnesium and its alloy components either as an end finish or as a pretreatment layer for other coatings. They are intended to

— improve the corrosion resistance during transportation,

— improve adhesion to paints and other organic finishes,

— modify surface frictional properties so as to facilitate sliding.

Phosphate conversion coatings are produced by treatment with solutions, the main constituents of which are the appropriate dihydrogen orthophosphates, so as to enhance the corrosion resistance of the products. The following factors can affect the mass per unit area and apparent density of phosphate conversion coatings:

— the base material and surface condition of the components,

— mechanical and chemical pretreatment of the components,

— processing conditions for phosphating.

All phosphate conversion coatings of magnesium alloy components are more or less porous but can be sealed substantially by subsequent sealant processes.

Specification for phosphate conversion coating on magnesium and its alloys

This document specifies terms, definitions, requirements and test methods for phosphate conversion coatings which are usually applied to magnesium alloy components (hereinafter referred to as film).

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 2080, Metallic and other inorganic coatings — Surface treatment, metallic and other inorganic coatings — Vocabulary

ISO 2177, Metallic coatings — Measurement of coating thickness — Coulometric method by anodic dissolution

ISO 4519, Electrodeposited metallic coatings and related finishes — Sampling procedures for inspection by attributes

ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

For the purposes of this document, the terms and definitions given in ISO 2080 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

Phosphating conversion coatings

Stable compound coatings formed on the surface of products in phosphoric acid solution by chemical or electrochemical methods.

3.2

Phosphating conversion coatings as end finish

After phosphating pretreatment, the product shall be used as end finish.

3.3

Phosphating conversion coatings as pretreated layer

After phosphating pretreatment, the product shall be coated on the phosphate coating to form a new coating.

The following information shall be provided by the purchaser.

a) A description of the phosphate conversion coatings according to this document (see 6),

b) The sampling procedure, the acceptable quality limit or any other requirements and tests that deviate from IS0 4519,

c) The appearance of the surface,

d) Phosphating parameters,

e) The corrosion resistance requirement,

f) The quality, appearance and condition of magnesium alloy matrix, if any of these properties affect the film-forming ability and /or appearance of phosphate conversion coating,

g) Where applicable, technical measures to minimize the risk of hydrogen induced brittleness as defined by the user,

h) When phosphate conversion coating is subjected to dehydration heat treatment and paint baking, the dehydration temperature and time should be controlled.

Before phosphating treatment, the surface of the products shall be clean and free of any oxidation, scale or contamination (such as metal chips, grinding powder, oil, grease, lubricating oil, sweat or other pollutants that have adverse effects on the conversion process). Therefore, the product shall be cleaned in the cleaning agent, and pickling shall be carried out when necessary.

The phosphate conversion coating shall be declared according to Table 1.

Table 1 — Declaration of phosphate conversion coating

The coating marks shall be expressed in the order of coating name, this standard number, composition system and post-treatment symbol.

Examples of markings are as follows:

Phosphate conversion coating, the standard number (ISO...), Composition system (Znph) and Post processing symbol (t)

Example: Phosphate conversion coating ISO 22230- /Znph/t1

The performance requirements are based on the agreement of supplier and demander, generally divided into the performance of phosphating conversion coatings as end-finish and phosphating conversion coatings as pretreated layer.

The appearance of the phosphate conversion coating shall not contain white spot, the phosphate conversion coating shall be continuous, there shall be no ash hanging, and the appearance and color shall be uniform. The specific appearance and color requirements can also be determined by the supplier and demander through standard samples.

The corrosion resistance is characterized by neutral salt spray test (NSS) and is recommended to be in accordance with Table 2. The corrosion grade shall be agreed by the supplier and the demander. The salt spray test shall be conducted in accordance with ISO9227. The demander shall conduct neutral salt spray test (NSS).

Table 2 — Declaration of phosphate conversion coating

The post treatments of phosphating conversion coating shall be agreed by the supplier and demander, and indicated in the contract. The symbols of post treatments shall be in accordance with Table 3.

Table 3 — Symbols of post treatment