Aluminum is a lightweight, durable metal known for its corrosion resistance and high conductivity, making it essential for industries such as construction, aerospace, and automotive. Production of aluminum and its alloys is a major industry in Oman and the Gulf region, and worldwide. Aluminum smelting is the process of extracting pure aluminum from its oxide, typically using the Hall–Héroult process, where alumina is dissolved in molten cryolite and electrolyzed to produce aluminum metal. The anode plant utilizes the Söderberg method to produce anodes for the reduction line. A critical component in the anode is the Clad, also called the Electric Transition Joint (ETJ). The Clad connects the upper part of the stem (made of aluminum) to the lower part, known as the bracket (made of steel). The middle section of the Clad contains titanium, which is explosion-welded on one side and MIG-welded on the other, creating a bond between the upper and lower parts.
Some regional smelting plants have reported repeated failures in the anode Clad, which are characterized by elongation or bending. These defects could be caused by uneven stress distribution, high temperatures, and high electrical currents. Clad failure resulting in a tilt of more than 16° in the stem can lead to smelting process failure. In one regional plant, there has been a significant increase in Clad failures in recent years, despite no reports of such failures in earlier years. The main aims of this study were to investigate the Clad failure problem in aluminum smelters, identify the main causes, and recommend appropriate solutions. Various methods were used to investigate the Clad failure, including visual inspection, X-ray inspection, chemical composition testing, welding strength testing, tensile testing, shear testing, and finite element analysis (FEA).
The primary causes of Clad failure were identified as lack of fusion, lack of penetration, and porosity in the welded joints, as revealed through visual and X-ray inspections of sectioned samples. FEA of different sections of the Clad, considering the welding layer under mechanical, thermal, and electrical loads, showed that with proper welding quality, the assembly can handle all applied loads without failure. To prevent future issues, it is recommended that welders possess advanced skills (proper licensing and MIG welding experience), welding parameters (such as current, welding speed, and shielding gas) be tightly controlled, and environmental factors (like dust and humidity) be minimized.