Register

Canadian Welding Bureau (CWB) Level 3 Practice Exam

Access More Questions
Why is oxide thickness on an Mg–Al alloy surface thicker than on a Mg-free alloy for the same thermal and mechanical history?
Correct Answer:
The oxidation rate of Mg-containing alloys is greater than for Mg-free alloys.
Explanation:
Oxide thickness tracks how fast oxidation proceeds under the given history. Magnesium-containing alloys oxidize more rapidly because Mg readily forms oxides (like MgO) that are less protective and allow faster diffusion of ions through the scale. This means the oxide layer can keep growing during the same heat exposure, producing a thicker film. In contrast, a Mg-free alloy, especially one with aluminum, tends to form a denser, more protective Al2O3 scale that slows further oxidation and keeps the oxide thickness thinner. So, the key idea is that Mg-containing alloys have a higher oxidation rate, leading to thicker oxide layers under the same thermal and mechanical history.

Access more questions from this quiz

Continue to Canadian Welding Bureau (CWB) Level 3 Practice Exam for more practice questions and the full quiz experience.

Access More Questions