Bro its a simple answer.
Use Marshmallow or above version ROM > insert your memory card. Then a pop-up will come. Select> use format sdcard as internal. Then your memory card would be used as adoptable internal storage. Make sure that you use a fast memory card class 10 or more. You data on memory card will be erased and you won't be able to use as portable drive unless and until you format it as external.