Which of the following conditions is NOT ideal for welding?

The ideal conditions for welding are crucial for ensuring a strong and reliable joint between the metals being joined. In this context, the presence of oxides is detrimental to the welding process. Oxides form a layer on the surface of metals, which can create barriers to heat transfer and may prevent the metals from fusing properly. This contamination can result in weak welds, porosity, or even complete failure of the joint.

In contrast, same microstructure in metals facilitates a harmonious union during the welding process. When two metals share a similar microstructure, they are more likely to bond effectively, as their atomic arrangements will be compatible. Clean surfaces free from dirt ensure that there are no foreign materials interfering with the weld pool, allowing for a stronger bond. Lastly, good quality metals without internal impurities ensure that the weld can achieve its maximum strength, as impurities can lead to defects in the weld.

Therefore, the condition that is not ideal for welding is the presence of oxides, as it directly undermines the quality of the weld joint by introducing barriers that disrupt the necessary fusion.