Effect of Welding Current on Microstructure and Properties of Aluminum Bronze Powder Plasma Cladding Layer

Literature Overview and Research Background

The study titled "Effect of Welding Current on Microstructure and Properties of Aluminum Bronze Powder Plasma Cladding Layer" investigates how varying plasma arc welding (PAW) current parameters influence the metallurgical microstructure, mechanical properties, and corrosion resistance of aluminum bronze (Al-Bronze) powder cladding deposits. Aluminum bronze alloys, such as CuAl10Fe5Ni5 and CuAl10Fe5Mn5, are widely employed in marine engineering, chemical processing, and hydraulic components due to their exceptional wear resistance, cavitation resistance, and corrosion resistance in seawater environments. The research systematically examines the influence of plasma current levels—typically ranging from 100 A to 300 A—on dilution ratio, grain morphology, phase composition, hardness distribution, and overall deposit quality. This work is particularly relevant for engineers involved in surface engineering of hydraulic machinery, ship propellers, and chemical equipment where aluminum bronze overlay layers are applied to carbon steel or low-alloy steel substrates.

Core Technical Points and Microstructural Analysis

The plasma transferred arc (PTA) powder cladding process offers several advantages over conventional arc welding methods, including a narrow heat-affected zone, reduced dilution, and precise control over deposition geometry. The key technical parameters investigated include plasma arc current, travel speed, powder feed rate, arc voltage, and shielding gas flow rate. The welding current directly governs the heat input per unit length, which in turn controls the solidification rate, cooling rate, and dilution between the substrate and the cladding material.

At lower current levels (100–150 A), the heat input is relatively low, resulting in higher cooling rates and finer grain structures. However, insufficient heat input may lead to incomplete melting of the powder, porosity formation, and poor bond strength at the interface. At intermediate current levels (150–200 A), an optimal balance is achieved between heat input and cooling rate, producing equiaxed grain structures with good mechanical properties. At higher current levels (200–300 A), excessive heat input leads to coarser grain growth, increased dilution from the substrate, and potential softening of the cladding layer due to the formation of iron-rich phases.

The microstructural analysis reveals that the aluminum bronze cladding layer typically consists of a solid solution matrix of Cu-Al (γ phase), Fe₂Al₅ intermetallic compound (η phase), and Cu₃Fe phase. At optimal current levels, the η phase is finely dispersed within the Cu-Al matrix, providing excellent wear and corrosion resistance. However, at high current levels, the increased dilution introduces excess iron into the deposit, promoting the formation of brittle Fe₂Al₅ and Cu₃Fe phases in larger quantities, which degrades toughness and corrosion resistance.

The dilution ratio is a critical quality indicator in PTA cladding. For aluminum bronze overlays, the acceptable dilution range is typically 10–20%, depending on the application requirements. Excessive dilution (>25%) significantly reduces the corrosion resistance in chloride-containing environments, as the substrate carbon steel contributes ferrite and pearlite phases that are susceptible to galvanic corrosion.

Process Optimization and Quality Control

Based on the study findings, the optimal process window for aluminum bronze powder plasma cladding is identified as follows:

• Plasma current: 160–200 A
• Travel speed: 150–250 mm/min
• Powder feed rate: 50–80 g/min
• Arc voltage: 18–24 V
• Shielding gas: Argon at 10–15 L/min
• Powder-to-arc distance: 5–8 mm

Quality control measures must include cross-sectional metallographic examination to verify bond integrity and dilution, hardness mapping across the deposit cross-section, and corrosion testing in simulated service environments (e.g., 3.5% NaCl solution at 60°C). The bond strength between the cladding layer and substrate should exceed 200 MPa for structural applications, as specified in relevant standards such as ASME IX and NB/T 47014.

Common defects observed at suboptimal current levels include:

1. Porosity at low current — caused by incomplete powder melting and trapped gas.
2. Cracking at high current — due to high dilution and thermal stress concentration.
3. Undercut at excessive travel speed — resulting from insufficient heat input per unit length.
4. Excessive dilution at high current — leading to property degradation and potential failure in corrosive environments.

Engineering Practice Implications and Study Insights

From an engineering practice perspective, this study underscores the importance of process parameter optimization in achieving reliable aluminum bronze cladding performance. In marine applications, such as propeller and rudder repair, the cladding layer must withstand cavitation erosion, abrasion from sand-laden water, and corrosion in seawater. The optimal current range identified in this study provides a practical baseline for field welding procedures.

For pressure vessel and piping applications where aluminum bronze overlays are specified for corrosion resistance in sulfuric acid or hydrochloric acid environments, the dilution control is paramount. Engineers should mandate multi-pass cladding with interpass temperature control (typically below 150°C for aluminum bronze) to minimize thermal distortion and maintain consistent dilution across passes.

This literature provides valuable guidance for welding procedure specification (WPS) development and qualified welding procedure (WPQ) validation. The findings should be incorporated into qualification records per NB/T 47014 and ASME IX, ensuring that production welding parameters remain within the qualified range. Engineers involved in surface engineering design should pay particular attention to the current-dilution-property relationship when specifying aluminum bronze overlay requirements for critical components.