The explosive growth of new energy vehicles and energy storage has positioned battery tray welding technology at the core of manufacturing processes. Facing the dual challenges of aluminum alloy lightweighting and complex structures, this article delves into battery tray welding technologies, comparing the principles, performance metrics, and application scenarios of conventional fusion welding, friction stir welding (FSW), and laser welding. Through multi-dimensional analyses of heat-affected zones (HAZ), joint strength, corrosion resistance, and more, we present a comprehensive evaluation of the advantages and disadvantages of these welding technologies.

1-Technical Principle Comparison

a. Conventional Fusion Welding

Principle: Uses heat sources such as electric arcs or plasma arcs to locally melt the welding joint, forming a molten pool that solidifies into a weld upon cooling. Protective gases (e.g., CO₂, argon) or flux are required to prevent oxidation, and filler materials such as wires or rods may be added.

Characteristics: High molten pool temperatures and rapid cooling lead to coarse columnar grains. The heat-affected zone (HAZ) is wide, with insufficient metallurgical processes, resulting in defects like pores and cracks.

b. Friction Stir Welding (FSW)

Principle: Utilizes a high-speed rotating tool to generate frictional heat with the workpiece, bringing the material to a thermoplastic state. Mechanical stirring and plastic flow achieve solid-phase bonding without forming a molten pool or requiring filler materials.

Characteristics: Welding temperatures remain below 80% of the material’s melting point. Dynamic recrystallization forms fine-grained structures, resulting in dense, defect-free welds with low heat input and minimal deformation.

c. Laser Welding

Principle: A high-energy-density laser beam is focused on the workpiece surface. Heat conduction (power density <10⁵ W/cm²) or deep-penetration welding (power density ≥10⁵ W/cm², forming a keyhole effect) achieves material melting and bonding.

Characteristics: Extremely narrow HAZ, deep penetration, high welding speed, and precision capabilities. However, it is sensitive to material surface reflectivity and requires strict control of process parameters.

a- Conventional Fusion Welding b- Friction Stir Welding c- Laser Welding

Figure 1: Principles of Common Battery Tray Welding Technologies

2-Performance Metrics

a. Heat-Affected Zone (HAZ) Comparison

Key Analysis:

Conventional Fusion Welding: High heat input leads to wide HAZ, grain coarsening, and metallurgical defects (e.g., pores), significantly reducing material performance.

FSW: Solid-phase bonding avoids molten pools. HAZ is divided into TMAZ and HAZ, with coexisting fine grains (NZ) and localized deformation (TMAZ).

Laser Welding: Ultra-narrow HAZ (0.1–0.5 mm) due to high energy density and rapid cooling, but keyhole effects may impact microstructural uniformity.

b. Joint Strength Comparison

Key Analysis:

Conventional Fusion Welding: Rapid solidification causes coarse grains and defects, significantly reducing joint strength. For example, MIG-welded aluminum alloys exhibit only 72.8% of the base material’s tensile strength.

FSW: Dynamic recrystallization forms fine grains (NZ), but TMAZ grain deformation and HAZ phase dissolution may create weak zones.

Laser Welding: High cooling rates suppress grain coarsening, yielding weld strength close to the base material.

c. Corrosion Resistance Comparison

Key Analysis:

Conventional Fusion Welding: Coarse grains and defects lead to preferential corrosion in HAZ and fusion lines.

FSW: NZ exhibits superior corrosion resistance due to fine grains and homogenization, but HAZ grain coarsening and secondary phase precipitation (e.g., Fe-containing phases) may create corrosion-sensitive zones.

Laser Welding: Narrow HAZ and uniform microstructure reduce active corrosion sites, but surface oxidation layers must be managed for optimal corrosion resistance.

3-Application Scenarios

a. Conventional Fusion Welding

· Applicable Areas:

Frame-to-Baseplate Connections: Used for welding the main structure of battery trays, such as aluminum profiles in BYD and BAIC models.

Edge Beams and Small Component Repair Welding: Suitable for complex or spatially restricted areas (e.g., edge beams, stiffeners) requiring supplementary welding with other processes (e.g., FSW).

· Suitable Workpieces:

Thick plates (e.g., steel trays or thick aluminum plates).

Non-sealed auxiliary structures (e.g., battery pack corner fixtures).

· Suitable Materials:

Aluminum Alloys: 6xxx series (e.g., 6061-T6) for thick plates, though joint strength is low (70%–80% of base material).

Steels: Cost-effective but heavy for steel battery tray frames.

· Limitations: High heat input causes significant deformation, unsuitable for high-precision or thin-plate welding.

b-Friction Stir Welding (FSW)

· Applicable Areas:

Baseplate Splicing: Long-seam splicing for aluminum trays, e.g., integrated cooling channel structures (Guangdong Walmate Tech case).

High-Sealing Zones: Battery tray-to-enclosure joints (e.g., Geely and XPeng models use double-sided FSW for sealing).

Complex Profile Connections: T-joints or hollow profiles (self-supporting via dual-shoulder FSW).

· Suitable Workpieces:

Aluminum extruded profiles (e.g., 10mm-thick baseplates with 2mm wall double-layer designs).

Dissimilar material welding (Al/Cu, Al/Mg), requiring specialized process optimization.

· Suitable Materials:

Aluminum Alloys: 6xxx series (6061-T6, 6005A-T6, 6063-T6), achieving 80%–90% base material strength.

Magnesium Alloys: Lightweight trays (e.g., Ruixiang Tech case), but heat input must be controlled to prevent grain coarsening.

· Technical Advantages: Solid-phase bonding avoids fusion defects, ideal for lightweight and high-sealing applications.

c-Laser Welding

· Applicable Areas:

High-Strength Steel Tray Critical Welds: High-stress zones (e.g., battery tray-to-body connections).

Precision Seal Welding: Cover plate seal welding (up to 40 mm/s speed with minimal HAZ).

Thin-Plate Splicing: Efficient splicing for thin aluminum/steel plates (<3mm), minimizing deformation.

· Suitable Workpieces:

High-precision, automated production lines (e.g., robotic laser welding systems).

Complex geometries (e.g., curved seams) requiring dynamic positioning systems.

· Suitable Materials:

High-Strength Steels: Tensile strength ≥1000 MPa, retaining 95% of base material strength.

Aluminum Alloys: Require surface pretreatment (e.g., anodizing) to reduce reflectivity, increasing costs.

· Limitations: Multi-pass welding for thick plates (>8mm aluminum), lower efficiency than FSW.

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