Core Factors Affecting the Performance of Aluminum Welding Locomotives

The performance of aluminum welded locomotives is directly governed by material properties and alloy selection. Different aluminum alloys significantly impact weldability and strength. The 6000 series (such as 6061) has excellent weldability and is commonly used in the body structure of aluminum welded locomotives. The 7000 series (such as 7075) is strong but prone to cracking and requires a specific welding wire and preheating process. The heat treatment state of the material is also critical. The T6 state alloy softens easily after welding and requires post-welding aging treatment to restore structural strength. The annealed state material has good plasticity but poses a higher risk of welding deformation.

The welding process and parameter control directly determine the joint performance of aluminum-welded locomotives.Friction stir welding (FSW) can increase the strength of the aluminum welded locomotive's large plate joint to 90% of that of the base material. Thus, aluminum welded locomotive manufacturing is the preferred process. In the MIG welding process for aluminum welded locomotives, it is necessary to strictly control the current and voltage (e.g., 180–220 A) and the gas protection (e.g., high-purity argon at 15–20 L/min) to prevent oxidation of the inclusions. Although laser welding has a small heat-affected zone, the assembly precision requirements are extremely high (gap ≤ 0.1 mm), if the aluminum welding locomotive process parameters deviate (e.g., if the FSW speed is insufficient), the joint strength will decrease by more than 30%.

The structural design and service environment pose two challenges to the performance of aluminum welded locomotives. Butt joints are ideal for the main load-bearing structure of aluminum welded locomotives due to their uniform stress distribution. However, lap joints require precise control of the lap length to prevent stress concentration. Additionally, when the wall thickness of the hollow profiles used in aluminum welded locomotives is less than 2.5 mm, the welding deformation can easily exceed 1.5 mm/m. In an oceanic climate with a Cl- concentration >100 ppm, aluminum welded locomotives will accelerate corrosion. If the Cl- concentration is >100 ppm, it is necessary to use a 5000 series alloy and increase the passivation treatment. Under temperature fluctuations, the difference in thermal expansion between aluminum and steel may cause fatigue cracks in aluminum welded locomotives, so it is necessary to reserve an expansion gap.

The manufacturing quality and maintenance strategy are key to ensuring the full-cycle performance of aluminum welded locomotives. The oxidized layer on the surface of aluminum welded locomotives must be removed before welding to a roughness of Ra ≤ 1.6 μm; otherwise, the strength will decrease by 50%. Key welds must be inspected using ultrasonic testing (defect equivalent ≤ φ 2 mm).During service, the key welds must be tested with magnetic particles every year. The anticorrosive coating must be recoated every five years, and the secondary welds must be reworked ≤2 times to avoid strength degradation caused by coarse grain size. The performance risk of aluminum welded locomotives can be systematically controlled through EN 15085 certification and other standards.