How to lock SD card on Samsung Android mobile?
You can use audio file manager. Download Google play. After download open the app . you need touch 5 second up of the app. Come new page then you type your password. When you give password you see hide.
Samsung doesn't offer a way to protect your SD card with a password. You can encrypt your phone through Settings > Security > Encrypt Phone and that's it. To add a password to the SD card, you will have to download and install third party applications from the Google Play.
Google Play SD card lock apps: https://play.google.com/store/search?q=sdcard+password&c=apps&docType=1&sp=CAFiEQoPc2RjYXJkIHBhc3N3b3JkegIYAIoBAggB:S:ANO1ljIHWRI