The joining on advanced high strength steel (AHSS) and aluminum alloys by resistance spot selding is highly sought after due to the benefits these joints can bring, mainly improvements in the strength to weight ratio of the body in white design. But, both AHSS-AHSS and AHSS-Al joints bring forth their own set of challenges. First, similar metal welds are very hardenable and exhibit low toughness due to their rich chemistry. The dissimilar welds have different physical/mechanical properties that promote the formation of brittle intermetallic phases. This study addresses the use of interlayer technology to improve the weldability of these joints and to improve their mechanical performance.
The base materials used in this study were 1.2-mm thick aluminum alloy AA6022-T4 and 1.6-mm-thick Al-Si-coated press-hardened boron steel, Usibor« 2000 (AHSS). The interlayer materials used were in 100 Ám foil form consisting of low carbon steel, 99.9% purity nickel, nickel – 10 wt.% iron for the AHSS-AHSS. For the AHSS-Al joint, the foil thickness for the materials was 250 Ám. The materials used were aluminum 1100, 99.9% purity nickel, nickel – 10 wt.% iron, low carbon steel, 304 stainless steel (SS) and 430 SS. RSW was done using an OBARA« Corp medium frequency direct current (MFDC) resistance spot welder.
The AHSS-AHSS joint with interlayer exhibited excessive expulsion thus achieving poor mechanical performance. The use of incremental energy to the nugget provided minimal indentation and notch geometry that improved the fracture mode and fracture energy.
The AHSS-Al joint was only achievable using interlayers. The addition of the interlayer material improved the joule heating that occurs at the interface promoting better joining. The mechanical performance improved greatly with the use of higher Cr alloys when compared to those with smaller additions.
The mechanical performance of the AHSS-AHSS joint was improved with the use of parameter optimization and interlayer material, while the AHSS-Al mechanical performance was improved through the use of proper interlayer material selection.
Keywords: RSW, AHSS, Aluminum, Mechanical Performance, Interlayers