i had searched on the dictionnary and i found that both of them are adverbs, but as chinafan said it depend of the sentence; for example when you say he speak aloud it mean ( il parle à haute voie) and when you say he speak loudly it mean (il parle bruyemment) which mean aloud=à haute voie and loudly=bruyemment hope you understand the french betweem brackets .but i will do another search .ok bye

Aloud simply means what they say is audible. A common example is to "read aloud" which means to say what you read. Loudly is a description of the level of noise caused by something or someone. It could be considered the opposite of quietly. If someone were to speak loudly they are making more noise than necessary.

I had searched and I found that aloud is only the long form from the word loud and loudly means the same but it depends for the sentence. For example: He speak very loud or He speaks very loudly. I think it depends on the grammar but I´m not sure at all.