Hello Torlon!
Migrating AX Databases without change de domain is easy.
Just detach the databases from de actual server and attach it into the new SQL Server instance. Another way is to use the backup/restore proccess.
You have to verify the permissions for the servisse accounts, be sure to configure the same servisse accounts for the new SQL Server instance.
After attach or restore de database and configure the permissions you have to change de AOS configuration using the Server configuration utility. Click the Databases tab and change the database server name to the new SQL Server instance.
Following links can help you: