In PyCharm, the automatic import suggestions are usually based on shared libraries. Unfortunately, like you said, PyCharm doesn’t automatically recognize custom aliases like tf for tensorflow. I did find a workaround method that can allow you to configure PyCharm to recognize your input. You must use "Live Templates" for custom text.

Steps to re-create for tensorflow:

1. Go to File > Settings in PyCharm.

2. Navigate to Editor > Live Templates.

3. Click the + button to add a new live template.

4. Set the abbreviation to trigger the import. This will be used as the shortcut you want to type every time. For this example, set it to 'tf'

5. In the Template text area, write the statement you want. This will be what your shortcut will be replaced with. For this example, set it to 'import tensorflow as tf'

6. At the bottom, click 'Define' to set the language you want this to be usable in. Select Python.

7. Apply the changes and press 'OK'

This should allow you to type 'tf' and press tab, setting in the text 'import tensorflow as tf'.