Low fixed-rate mortgages have helped many first-home-buyers but they have also created an economic time bomb that could explode in three years. Westpac, Australia's second biggest bank, has revealed that between September 2020 and March this year, 32 per cent of borrowers fixed their mortgage rate. That was a dramatic rise from 23 per cent in the six months leading up to the onset of the Covid pandemic in March 2020. Since then, a higher proportion of Westpac borrowers have also fallen behind on their mortgage repayments despite the record-low interest rates. Westpac, Commonwealth and NAB a...