Is a friend required to offer expiation for his oath to achieve reconciliation, or is he not obliged to do so since he was angry when he swore?

It is not permissible for a Muslim to abandon his brother for more than three days. If he meets him and greets him, and the other person returns the greeting, then they both share in the reward. If he does not return the greeting, then he has incurred sin, and the one who initiated the greeting is absolved from the abandonment. The friend who abandoned without a legitimate Sharia reason must repent and offer an expiation for an oath.

An oath sworn in anger is binding if the person is aware of what he is saying, but it is not binding if his anger is so severe that he is unaware of what he is saying.