GB/T 39495-2020 in English

Analysis of the core content of the standard

GB/T39495-2020 systematically standardizes the technical system of chromium-free chemical conversion coatings for aluminum and aluminum alloys for the first time, focusing on solving the environmental pollution problems of the chromate process. The standard defines three major application types of conversion coatings:

Key Technical Indicators

1. Pretreatment Requirements

The standard stipulates that chrome-free cleaning agent must be used for surface pretreatment, the surface roughness must be controlled at Ra≤0.8μm, and the residual oil should be <5mg/m².

2. Conversion Liquid Control

The pH value of the conversion liquid ranges from 2.5-5.0, the temperature is controlled at 20-40℃, and the processing time is 1-10 minutes. It is particularly prohibited to use solutions containing hexavalent chromium or trivalent chromium.

Innovation of detection methods

Neutral salt spray test specification

Perform NSS test according to GB/T10125, Type 1 film requires ≥168h without substrate corrosion, Type 2 film ≥72h, and Type 3 film ≥24h. Rating is based on the 9-level standard of GB/T6461.

Implementation recommendations

1. New production lines should give priority to titanium-zirconium composite system conversion liquid
2. The drying temperature of the no-clean process needs to be controlled in the range of 60-80℃
3. Regularly test the Zr²⁺ concentration of the conversion liquid (recommended ≥1.2g/L)

Technology evolution analysis

This standard promotes the transformation of my country's surface treatment industry from the chromate era (1980s-2010) to the multi-composite chromium-free system (2010-present), and will develop towards nano-composite membrane technology in the future.