Will rhode island red and black australorp hens go broody?

Rhode Island and Australorp hens may go broody but don't expect it. In raising Australorps for 15 years I've maybe had 1 hen every 3-4 years go broody and I've had usually about 25 Australorps each year. It may happen but I wouldn't "put all my eggs in one basket!" I can say that both breeds you have do have a very high fertility rate and should hatch easily in an incubator.