The Influence of Ultrasound Enhancement during Friction Stir Welding of Aluminum to Steel

Abstract

The innovative joining process of friction stir welding (FSW) offers a wide range of advantages for welding similar as well as dissimilar materials. Even for the field of poorly weldable material combinations like aluminum to steel with their strongly differing physical properties the method of FSW proved its capability for realizing dissimilar joints with tensile strengths up to more than 80 % of the aluminum base material. Trying to improve this value and other properties of the joints several approaches for hybrid friction stir welding processes were tested in the scientific community, whereas the ultrasound enhancement of FSW (USE-FSW) looked as one of the most promising reaching good results. To gain a deeper knowledge of the influence of the ultrasound on the friction stir welds different investigations were carried out in this paper. Therefore the method of USE-FSW was applied on two dissimilar aluminum/steel-joints with varying carbon content of the steel in this work. The material combinations AA6061/SAE1006 and AA6061/SAE1045 were welded successfully with and without additional power ultrasound. Afterwards a comparison between FSW-and USE-FSW-joints was carried out regarding the microstructure of the nugget and interface (IF) by light-microscopy as well as scanning electron microscopy. Furthermore the mechanical properties were characterized in a first step.

Investigations on Corrosion Properties of Ultrasound‐Enhanced Friction‐Stir‐Welded Aluminum/Dual‐Phase Steel Joints

“…The positive values measured in air (Figure 4) change to only negative values in the electrolyte, starting at about À0.3 V shortly after the immersion and declining continuously to À0.45 V within the first 10-15 min and then further to À0.51 V. This points to an activation of the steel leading to an OCP value that is more negative than that of the AA6061 Al alloy after 20-30 min. A similar behavior was observed for the steels SAE1006 and SAE1045, [23,25] but it is different to that of aluminum/magnesium hybrid joints, where an OCP difference of 0.9 V was measured between the base materials in the sodium chloride electrolyte similar to the Volta potential difference in air. [19,20,22] The OCP curves of the nugget area are nearly identical to those of the AA6061 aluminum base alloy.…”

“…These results are in accordance with investigations on other aluminum/steel hybrid joints. [23,24] 3.1.2. Radiography (X-ray)…”

“…These findings are in accordance with the results on AA6061/SAE1045 joints and AA6061/SAE1006 joints. [23,25]…”

“…This behavior is different to that of earlier investigated aluminum/steel combinations with SAE1006 and SAE1045 steel, where the nugget area shows an anodic shift of the E oc compared to the OCP measurements and corrosion current densities that are lower than that of the aluminum base alloy. [23,25] The corrosion current density of the nugget area shows some influence of the processing conditions as the value on the FSW joint is higher than those on the USE-FSW joints (Figure 6). This may be attributed to the amount of steel particles within the measured area.…”

A new physical simulation tool to predict the interface of dissimilar aluminum to steel welds performed by friction melt bonding

“…Therefore, welding is highly preferred for joining dissimilar metallic materials into a hybrid structure. One of the most attractive hybrid structures for the automotive industry consists of aluminum and advanced high strength steel (AHSS), as their combination reduces the weight of the structure and maintains the high crashworthiness [4,5]. However, due to the high reactivity between aluminum and steel in liquid state, there are limitations for the application of classical welding methods to join these materials.…”