Question

identify the following weld defect.

porosity
whiskers
cracking
cold start
undercut

Explanation:

Analyze the weld cross-section

Using the Welding Defects knowledge point

The provided image shows a cross-sectional macrograph of a fillet weld on a T-joint. Looking closely at the toe of the weld on the vertical member, there is a groove-like depression melted into the base metal right at the edge of the weld bead, which has not been filled by the weld metal.

Identify the defect characteristics

Using the Welding Defects knowledge point

A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal is the classic definition of an undercut.

Let's evaluate the options:

• Porosity: Cavities or gas pockets within the weld (not visible here).
• Whiskers: Unmelted electrode wire protruding through the root (not present).
• Cracking: Linear fractures (none visible).
• Cold start (or cold lap): Lack of fusion where weld metal rolls over without fusing (the image shows actual melting into the base metal, creating a sharp notch/groove, which is characteristic of an undercut).
• Undercut: A groove melted into the base metal next to the toe of the weld that is left unfilled. The notch at the upper toe of the fillet weld clearly matches this defect.

Answer:

• Porosity
• Whiskers
• Cracking
• Cold start
• Undercut (Correct answer)