Failure Analysis of Dissimilar Metal Weld Joint of an Air Spring Bracket within an Automotive Active Seat Suspension System

In modern four-wheelers, seat suspension systems play a crucial role in enhancing occupant comfort by mitigating the effects of road unevenness and vibrations. Among these systems, active suspension mechanisms offer advanced performance through complex assemblies involving welded, riveted, and bolted joints. This study investigates the failure of an air spring bracket - a critical component of a pneumatic active suspension system - manufactured by Gas Metal Arc Welding (GMAW) of two dissimilar ferrous materials which are likely to be SAPH440 and S355J2. These different materials were used based on mechanical properties required to perform by their particular part. System level validation tests were conducted to ensure the reliability of the seat suspension system. The one of the validation tests is continuous cyclic fatigue test which is carried out on the complete seat assembly. However, during vibration / cyclic endurance testing, premature failures were observed near the weld joints. Detailed failure analysis using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and optical microscopy revealed cracks and discontinuities at the weld interfaces. The microstructure in the heat-affected zone (HAZ) exhibited a mixed ferrite-pearlite-bainite structure with grain coarsening. The fractography reveals the cleavage type and river type fracture morphology which indicates the part failed due to brittle fracture. Inadequate welding of SAPH440 steel can lead to issues such as cracking, distortion, and poor fusion due to its high carbon content and inadequate heat control. The failure analysis study identified that less fusion control of welding parameters and associated thickness and carbon compositions variation which significantly contributed to the component’s fatigue failure. Preventive strategies, including the optimization of sectional thickness and design changes for uniform stress distribution are proposed to improve the reliability of welded assemblies.