You can use songs for ringtones on Android phone by making use of the Ringdroid app for android. I use the app alot to set ringtones on my Infinix hot 2 android 5.1 smartphone.
It is simply an android ringtone app that lets you create personal customized ringtones, alarms, and notification sounds from existing music/audio files on your Android phone. You can even use the app to record new audio clip and use it as a ringtone. The app also lets you assign ringtones to any phone contact with ease.
How To Use Ringdroid App To Set Songs as Ringtones on Android
==> Open the app, tap the three dots at the top right hand corner of the screen and tap “Show all audio”
==> Scroll down to the song you want to use as ringtone or use the search tool
==> Tap on the song and wait till it loads
==> Drag the markers at the top and below the waveform, to set the start and end time of your ringtone
If you only want to use it as a ringtone for a contact eg your wife/husband, tap on Assign to contact and select the contact from the list displayed.
I hope this helps.