Look at the Iron Man film series.
Iron Man: 585,174,222.
Iron Man 2: 623,933,331
Iron Man 3: 1,199,002,239
The Iron Man films were more successful than Thor, but look at that big boost between Iron Man 2 and 3. The Avengers gave Iron Man a big boost. So do you think Thor 2 will make it past 1 billion?