Administrators say the Dolgarrog Aluminium factory in the Conwy Valley in north Wales is to close.
Dolgarrog produces aerospace and commercial sheet coil and plate
It had been hoped a new buyer could be found for the plant which employs around 170 workers.
Dolgarrog Aluminium produces a range of products, turning over £19m last year, and is a major employer in the area.
Administrators KPMG had said they hoped to sell the plant when they were appointed last month but they are now starting to wind the operation down.
Dolgarrog Aluminium was set up five years ago following a management buy-out of the former Alcoa plant and it is Britain's only integrated casting and rolling aluminium mill.
The company celebrated its 100th anniversary of aluminium making on the site this year.
A KPMG spokeswoman said some employees were told on Wednesday they would be made redundant.
"We had been hopeful we'd be able to find a buyer for the business but those interested in buying couldn't come up with the necessary funds," she said.
"The process of winding down means not everybody will leave immediately but all the jobs will go when the winding down process is complete."
Plaid Cymru Aberconwy AM Gareth Jones - who said he was holding talks with Deputy First Minister Ieuan Wyn Jones - said news that the plant was to close was a "shock" and a "serious blow".
"The loss of 170 jobs is something that we can ill afford," Mr Jones said.
In a statement, Ieuan Wyn Jones said: "We have worked extremely hard to try to secure a future for Dolgarrog - and I give my commitment that we will continue to do so.
"I have personally been in touch on many occasions with senior management at the plant and will, of course, continue close co-operation with the administrators.
"The assembly government provided financial assistance five years ago to support the continuation of the business and, very recently, we provided loan funding to enable the business to continue while the administrators sought a buyer for the business.
"We will look to support any viable opportunity that emerges - even at this late stage - to keep this business alive."
The package had been agreed in principle involving Finance Wales, a Welsh Assembly Government subsidiary.