the reason for such a hardfault can be caused by a not properly working hardware or a wrong configuration of system or memory.
First of all, please ensure that the SDRAM is working correctly - try this memory-test.
If your hardware is different than the STM32F429 discovery or evalboard, please verify that the memory areas are adapted correctly (e.g. start address and range of SDRAM).
If the problem still exist, please let me know more details about your hardware.