Is an act that is legal is also and necessarily moral?

The two are not the same, though they often parallel each other. The law regulates a set of standards. Morality regulates a set of ethics. For instance, adultery is not illegal, but it could be argued that it is immoral. Corporations routinely are found not legally culpable for engaging in practices that could be considered immoral, like addicting people to cigarettes or failing to fix an auto problem that kills people because settlements cost less than the fix. On the flip side, demonstrators fighting for a just cause might be breaking laws but it could be argued that they are correct morally.