Hales eventually holed out for 147 on his Nottinghamshire home ground after opener Jonny Bairstow had made 139.
The crushing victory was England's third in the ODI series and means they have an unassailable lead with two games to spare.
Roy struck his 82 runs off just 61 balls and Morgan needed just 30 balls to compile his 67.
The current bowling attack comprising Kane Richardson, Andrew Tye, Jhye Richardson and Billy Stanlake has a combined bowling experience of 21 ODIs - a fact that has worked in England's favour. Only once in the 56-year history of List A cricket - when Surrey scored 496 for 4 against Gloucestershire at The Oval in 2007 - has any side scored more.
Bairstow plays a shot during the one-day worldwide on Tuesday.
In response, Australia fell well short of the record target, making 239 all out in 37 overs.More news: Denmark edges out luckless Peru
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The 242-run defeat was Australia's heaviest defeat in 47 years and 915 games of one-day cricket, surpassing a 206-run loss to New Zealand in 1986.
England are the hosts of the next year's ODI World Cup.
It seemed inevitable England would reach 500 but Hales and Morgan went in successive balls late on as Richardson got some belated reward and the run rate finally dropped.
Buttler followed shortly after, having been sent in up the order at four, before Hales and Morgan added 124 runs in just 59 balls. Certainly there were aspects of this match - mostly some outrageous hitting - that created an entertaining and memorable spectacle. The visitors will need to reverse history as only twice have teams breached the 400-run mark whilst batting second in ODIs. On the same ground where England plundered the previous record 444 for 3 against Pakistan in August 2016. In a series of social media posts, Ganguly wrote, "To see nearly 500 runs scored in 50 overs in England is scaring me, bout the health of the game and where it's going".
"We've got to bat against the top and against spin", said Langer.
"Sometimes you've just got to accept what you've got and be ultra-defensive from the start, put a few more fielders in front of the batsman's face and see if you can create a bit of pressure that way".