Wal-Mart donated $5 million Tuesday to help build the Smithsonian Institution’s planned National Museum of African American History and Culture on the National Mall.

The gift makes the world’s largest retailer one of the project’s “founding donors” who have given more than $1 million.

Construction is scheduled to begin next year for a $500 million museum on a five-acre site near the Washington Monument next year. The project is on track to open in fall 2015, Museum Director Lonnie Bunch said Tuesday.

“This opens the door for even more corporations to give money and give support,” Bunch said of Wal-Mart’s gift. “We’re looking for entities that care about questions of diversity and education in America’s history.”

The museum already is building its collection. It recently acquired a biplane trainer flown by the Tuskegee Airmen in World War II. It recently went on display at the National Air and Space Museum’s Virginia annex until it the black history museum is built.

The Smithsonian is working to privately raise about half of the $500 million cost for what will be its 19th museum. Congress has pledged to provide the other half of the funding. In 2009, the Bill and Melinda Gates foundation gave $10 million to help start the effort.

The campaign is still in its quiet phase, and Bunch would not say exactly how much money he has raised. But he said the museum is on track to raise about $200 million by the end of 2012. As of this month, he’s nearly half-way there, Bunch said.

Last year, former first lady Laura Bush joined an advisory board to help raise money for the museum project. Others who have helped raise funds include Oprah Winfrey, Quincy Jones, Brown University President Ruth Simmons and Target Corp. CEO Gregg Steinhafel.

Wal-Mart also supported construction of the Martin Luther King Jr. Memorial, which was recently dedicated in Washington. Fundraising for that $120 million project continued leading up to its dedication.

Bunch said the Smithsonian wanted to give the memorial groups space to complete its campaign but has also raised money at the same time because the projects are “complimentary.”

“Now that the King Memorial is finished, it will contribute to our success,” he said, “but the fact that they were still fundraising didn’t really hurt us.”