Adhesive Bonding Performance of GA Coated 590 MPa Tensile Strength Steels 2011-01-1052

Advanced high strength steels (AHSS) are becoming major enablers for vehicle light weighting in the automotive industry. Crash resistant and fracture-toughened structural adhesives have shown potential to improve vehicle stiffness, noise, vibration, and harshness (NVH), and crashworthiness. They provide weight reduction opportunity while maintaining crash performance or weight increase avoidance while meeting the increasing crash requirement. Unfortunately, the adhesive bonding of galvanneal (GA)-coated steels has generally yielded adhesive failures with the GA coating peeling from the steel substrate resulting in poor bond strength. A limited study conducted by ArcelorMittal and Dow Automotive in 2008 showed that GA-coated AHSS exhibited cohesive failure, and good bond strength and crash performance. In order to confirm the reliable performance, a project focusing on the consistency of the adhesive bond performance of GA-coated steels of 590 MPa strength level was initiated. The 590 MPa steels include 590R (complex phase, high yield to tensile ratio), 590Y (dual phase (DP)), and 590T (transformation-induced plasticity (TRIP)). Adhesive bonding was evaluated by lap shear tests at room temperature at Dow Automotive and ArcelorMittal Global R&D-East Chicago. Bonds were made with a crash-resistant structural adhesive, BETAMATE™ 1488. Additionally, the 590 MPa steels were evaluated after bonding with BETAMATE™ 1022DUS, a fracture-toughened structural adhesive, and BETAMATE™ 73305GB, a conventional, structural, hem-flange adhesive, to demonstrate the performance of adhesives with different moduli of elasticity. Lap shear testing was also conducted on GA-coated interstitial-free (IF), extra deep drawing steels (EDDS), bonded with the three adhesives, to determine if lap shear performance of GA EDDS can be improved with the new generation adhesives. X-ray diffraction (XRD) was used to measure the residual stress at the interface between the zinc coating and steel substrate as an indication of the interface bonding. This paper describes the results of this testing and demonstrates that crash-resistant structural adhesives can provide consistently good bonding for GA-coated AHSS and thus be used to reduce weight while maintaining or improving crash performance.