What type of weld would be most effective for joining two plates at right angles?

A fillet weld is specifically designed to join two surfaces that are at right angles to each other, making it the most effective choice for this scenario. This type of weld is applied to the outside corner or the inside corner of the two plates, effectively creating a triangular cross-section that allows for strong bonding between the joints.

Fillet welds are commonly used in various fabrication and construction applications because they provide good strength and can accommodate slight misalignments between the joined pieces. They are especially advantageous for connecting components in a T-joint configuration, which aligns perfectly with the requirement of joining two plates at right angles.

Other options like bevel welds and butt welds are better suited for joining edges of plates in flat alignment rather than at a right angle. A corner weld, while it may also seem appropriate for corners, typically refers to a specific application that might not be as effective as a fillet in terms of load-bearing and structural integrity at right angles.