Is there a chance to lose data if I switch RAID to AHCI

I have Windows 7. The boot drive is NON-raid SSD. I also have 2xHDD RAID1 (just data). RAID is Intel Matrix (or whatever the latest name for it).

I installed Windows in RAID mode

What might happen to the data if I change BIOS to AHCI?

I cant answer with 100% certainty, however you should not lose any data. Worst case, switching from RAID to AHCI would cause the drive to be unable to be read. If this were to happen, you could switch it back and everything should be copasetic. However, this is not likely to be the case. The controller should just pick up the disk as a single drive and not lose access or data.

As always when performing potentially damaging changes, make a backup.