A giant stockpile of aluminum that has crisscrossed the globe remains a puzzle for American executives and investigators trying to unravel the logic behind its movements.

A Dallas attorney’s correspondence suggests a surprising possibility: that the stash is a Chinese billionaire’s retirement fund.

Like all Chinese citizens, Liu Zhongtian, the 52-year-old chairman of aluminum behemoth China Zhongwang Holdings Ltd. , isn’t supposed to move more than $50,000 a year out of the Communist Party-led country. To get around the restrictions, Chinese nationals have used Hong Kong money changers to illicitly transfer cash between bank accounts, combined their $50,000 quotas to make large-scale transfers and even carried cash across borders in suitcases.

Mr. Liu developed an industrial-scale approach involving boatloads of aluminum which he stockpiled with plans to sell the metal over time, according to the Dallas attorney’s correspondence and people who have worked for Mr. Liu whose accounts are supported by shipping and corporate records.

Mr. Liu sought to establish companies that could control his wealth outside China and set up an office in Switzerland, according to a 2012 email from attorney Herman Randow of Dallas firm Munsch Hardt Kopf & Harr.