A Review on Al-Al/Al-Steel Resistance Spot Welding Technologies for Light Weight Vehicles

Abstract

The main focuses of automotive industries are to reduce weight, increase fuel efficiency, and reduce air pollution. To fulfill the demands of fuel economy, lowering the mass of the auto structure can be achieved by substituting steels with light weight materials (like aluminum (Al) and magnesium (Mg) alloys1) ) or steels combined with those. There are lots of advantages to use Al instead of steels; corrosion-resistance, nonmagnetic, no color change during heating, and mechanical properties of some of its alloys are superior compared to mild steel. Use of multimaterials in manufacturing process enables low cost production and improvement of joint strength. Al alloys and steels are the most important and indispensable construction materials. Uses of sounds joining technique of those materials ensure the low cost fabrication process to be employed. Welding of steel and Al is not a simple issue to be solved easily. Because conventional welding process resulted in brittle intermetallic compounds (IMC) which are detrimental to joint as it made joint brittle and weak 2) . Since electrical and thermal conductivity of aluminum alloys are significantly high; which required higher current (2.5 to 3 times as of steel), and shorter weld time. Consistency of uniform pressure and current are fundamental needs for Al resistance spot welding. Deterioration of electrodes is vital issue, which may occur due to non uniformity of pressure and current. Electrode erosion eventually leads to undersized welds which should be avoided by using proper surface coatings and treatments on electrodes. Aluminum has high tendency to react with oxygen in the atmosphere and form oxide films on the surface of metal. This oxide films has high resistivity and corrosion protection ability which resists forming weld nugget in RSW. Auhl and Patrick et al. 3) reported that breaking down of oxide layer and ensures proper weld nugget formation usually required high electrode pressure. Many researchers 3-7) demonstrated that surface cleaned with chemicals; resulted thinnest oxide layer which improves the electrode life. Among the other types of chemically treated surface conditions, pretreated/lubricated surface is the most effective to apply for mass production automotive application. Resistance Spot Welding (RSW) is the primary methods of joining automotive, which is beneficial due to low-cost, high speed production, and availability of multi-materials welding at a same time. Few researchers 8-10) reported that the main barrier to use RSW in Al vehicles is the degradation of electrode life. In this review paper, a few techniques of Al-Al/Al-Steel RSW and possible ways of overcoming the difficulties of welding processes were discussed.