Which of the following is a common effect of welding on base metals?

In welding, one common effect on base metals is increased brittleness. This phenomenon often occurs due to the rapid cooling and heating processes involved in welding, which can lead to the formation of hard and brittle microstructures, especially in certain types of steel and alloys. The heat affected zone (HAZ) adjacent to the weld can undergo changes that result in a reduction of toughness, making the metal more susceptible to cracking under stress or impact.

Understanding the thermal cycles that occur during welding is essential; these can lead to phase transformations in the metal's structure. If the cooling rate is too fast or the chemical composition of the base metal is not balanced for welding, the resulting microstructure might not provide the ductile qualities that are usually required for structural integrity. This increased brittleness can pose significant risks, particularly in applications where the base metal is expected to endure dynamic loads or harsh environments.

The other options represent effects that are generally not observed in welding. For example, decreased thermal expansion and enhanced ductility are not typical outcomes of welding, as the processes usually compromise the thermal and structural properties of the material. Improved electrical conductivity is also unlikely, as welded areas often develop non-conductive oxides or inclusions that can interrupt electrical paths in a material