아침에 will be "in the morning" and 아침이면 is "when it's morning." 아침이면 is basically the shortened version of 아침이 되면. Hope it helps :)

아침에 is the status of the morning. "in the morning". For example, I joined this website in the morning of today. 아침이면 is some conditions of the morning. For example, if it is the morning, i should have to wash my hands.

"면" is a subjunctive conjunctive particle. It could be translated "if" or "when" in English. - 비가 오면 집에 돌아가자. If it rains, let's come back home. - 아침이면 일어나 창 밖을 봅니다. If (When) it is a morning, I get up and look out the window. (It might be more natural to say "if a morning comes" in English but here I translated word for word. - 봄이 오면 꽃이 핀다. If (When) Spring comes, flowers blooms. - 눈이 오면 정말 좋을텐데. If it snowed, it would be really nice. - 그가 착한 사람이면 복을 받게 되어 있다. If he is a good man, he is supposed to be blessed.