Australian steel and aluminium exporters to the US will learn early on Friday whether they'll be hit by Donald Trump's new tariffs as part of his "America First" economic plan.

Prime Minister Malcolm Turnbull and key ministers have been engaged in a last-minute effort to seek an exemption for either Australia as a whole or individual companies such as BlueScope.

The other prospect is Mr Trump will at least include a review clause to allow countries to negotiate in the future.

The president's main trade adviser Peter Navarro said the proclamation would be signed at 7.30 AEDT on Friday in the White House Oval Office.

Mr Trump would be accompanied by a "bunch of men and women from steel country and aluminium country", Mr Navarro said.

"He'll sign the proclamations and within about 15 to 30 days the tariffs go into effect."

A week ago, Mr Trump announced plans for global import tariffs of 25 per cent on steel and 10 per cent on aluminium products, but there have been suggestions Canada and Mexico may get a honeymoon period or exemption.

Mr Turnbull told reporters on Thursday he had been making personal representations to Mr Trump for some time.

"I'll continue my advocacy at many levels, but megaphone diplomacy is rarely effective."

The government is holding out hope that a White House promise to consider exemptions on a "case by case" and "country by country" basis will include Australia.

BlueScope ships Australian steel to the US west coast to make into roofing products because of the high cost of freight from the east coast.

The US steel and aluminium trade is worth around $500 million a year to Australia.