These animals can usually be dangerous

1. These animals can be dangerous.

Sentence 1) can be glossed as:

2. These animals are sometimes dangerous. Or

3. Some of these animals are dangerous.

We can also add the adverb of frequency "sometimes" to sentence 1) to make it clear which meaning we intend to imply:

4. These animals can sometimes be dangerous.

Q: Can we use the frequency adverb "always" or "usually" with "can":

5. These animals can always be dangerous.

6. These animals can usually be dangerous.