Which of the following materials is typically used as a filler rod in welding?

Aluminum is commonly used as a filler rod in welding processes, particularly in the welding of aluminum components. Filler rods are essential as they help to fill the gap between the workpieces being joined, ensuring a strong and durable weld. In the case of aluminum, the filler rod is often made from the same or a compatible aluminum alloy, which allows for good metallurgical bonding and helps to maintain the integrity of the weld joint.

The other materials listed—plastic, wood, and rubber—are not suitable for use as filler rods in welding. They do not have the necessary properties to withstand the high temperatures involved in welding and would not create a strong or reliable weld joint. Using incompatible materials can lead to poor adhesion, weakened joints, and potential failure of the weld under stress.