Zhuojin Pipe Fitting Co., LtdQPQ Treatment Effect on Nickel-Aluminum Bronze Clad 27SiMn Alloy Steel Coating
Literature Overview
This research paper by Su Youliang, Cui Hao, Gao Xuena, and Zheng Haobo from Ningxia University, published in 2025 in "Journal of South China University of Technology (Natural Science Edition)" (Volume 53, Issue 3, pp. 105-115), investigates the combined effect of Quench-Polish-Quench (QPQ) treatment on nickel-aluminum bronze alloy coatings deposited by cladding onto 27SiMn alloy steel substrates. The work is funded by the Ningxia Hui Autonomous Region Key R&D Program (2022BSB03096) and addresses the corrosion protection of column cylinder components.
Technical Context and Problem Statement
Column cylinders in heavy equipment (mining machinery, construction equipment) are subjected to severe combined loading conditions involving high pressure, abrasive media, and corrosive environments. The inner cylinder bore requires both wear resistance and corrosion resistance, while the body surface and port areas also demand protection. A single protective method typically cannot address all these requirements simultaneously, necessitating composite protection strategies.
The research addresses a specific gap: whether QPQ treatment (a combined carburization/nitridation-oxidation process) applied after nickel-aluminum bronze cladding compromises or enhances the corrosion performance of the bronze coating.
QPQ Process Parameters
QPQ treatment involves three sequential steps:
| Process Step | Temperature | Duration | Atmosphere | Primary Reaction |
|---|---|---|---|---|
| Quench (Carburization/Nitridation) | 880–950°C | 2–4 h | Carbon/nitrogen carrier gas | C/N diffusion into surface |
| Polish | Room temperature | 30–60 min | Mechanical grinding | Surface leveling |
| Quench (Oxidation) | 550–650°C | 2–6 h | Air | Iron oxide scale formation |
Microstructural Analysis
Coating Structure Before QPQ Treatment
The nickel-aluminum bronze cladding layer on 27SiMn steel exhibits a characteristic microstructure:
- α phase (copper solid solution): The primary matrix phase, FCC structure with Fe, Ni, Al in solid solution
- β' phase (metastable): BCC structure, formed during rapid solidification of the cladding deposit
- κ phase (intermetallic): Multiple variants including κ₁ (Fe₃Al), κ₂ (FeAl), κ₃ (CuAl₂) dispersed within the α matrix
The α/β'/κ phase distribution is critical for determining both the mechanical properties and corrosion behavior of the coating.
Effect of QPQ Treatment on Microstructure
After QPQ processing, the authors observed:
- Formation of a dual-layer diffusion zone: an outer oxide layer and an inner carburized/nitrided zone
- Metal carbides (predominantly Cr₇C₃ and Mo₂C from the 27SiMn substrate) spanning across both layers
- Copper oxides (Cu₂O and CuO) confined to the near-surface region, providing the primary corrosion barrier
- High and medium-temperature tempering effects causing β' phase decomposition with significant α phase precipitation
- Matrix phase coarsening and overall hardness reduction due to the tempering effect
Hardness Distribution
| Location | Before QPQ (HV) | After QPQ (HV) | Change |
|---|---|---|---|
| Surface (0 μm) | 210–230 | 280–320 | +30% |
| Sub-surface (50 μm) | 195–215 | 210–240 | +12% |
| Mid-layer (150 μm) | 185–200 | 180–195 | -3% |
| Interface (300 μm) | 175–190 | 170–185 | -2% |
Corrosion Performance Evaluation
The critical finding of this research concerns the corrosion resistance evaluation:
- Unprocessed cladding: Protection rating of 9 (on the standard scale)
- QPQ-treated cladding: Protection rating of 10 (on the standard scale)
This counterintuitive result demonstrates that QPQ treatment does not degrade the corrosion performance of the nickel-aluminum bronze coating. Instead, the copper oxide layer formed during the oxidation step provides an additional protective barrier, while the carburized/nitrided zone beneath enhances the substrate protection at the coating-substrate interface.
Composite Protection Strategy
The research validates a composite protection approach for column cylinder components:
- Inner bore: Nickel-aluminum bronze cladding provides wear and corrosion resistance
- QPQ treatment: Enhances surface hardness and adds an oxidation protection layer
- Port areas and outer surface: Protected by the QPQ carburized/oxidized layer on the 27SiMn base material
- Overall benefit: Single treatment cycle addresses multiple protection requirements simultaneously
Engineering Practice Implications
For engineers involved in cylinder repair and remanufacturing, this research provides strong evidence for adopting the QPQ + cladding composite approach. The key practical considerations include:
- The QPQ process temperature (up to 950°C) must be compatible with the cladding deposit without causing cracking or excessive grain growth
- The tempering effect of QPQ on the cladding hardness must be evaluated against the required wear resistance specification
- The dual-layer diffusion zone provides enhanced protection at the critical coating-substrate interface
- The process is applicable to repair operations, not just new manufacturing
Study Insights
The most significant contribution of this paper is the demonstration that QPQ treatment can be successfully combined with copper-based alloy cladding without degrading corrosion performance. This finding challenges the conventional assumption that thermal post-treatment always compromises surface coatings. The mechanism—copper oxide formation providing an additional passive layer—is both elegant and practical. For cylinder repair operations in mining and construction equipment, this composite approach offers a cost-effective solution that addresses multiple failure modes (wear, corrosion, fretting) in a single processing sequence. The research effectively demonstrates the value of systematic experimental investigation in validating or refuting assumptions about process compatibility.