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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

For The Fiscal Year Ended December 31, 2004

OR

Commission File Number 1-3610

ALCOA INC.

(Exact name of registrant as specified in its charter)

201 Isabella Street, Pittsburgh, Pennsylvania 15212-5858

(Address of principal executive offices) (Zip code)

Registrant’s telephone numbers:

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months, and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  x

Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Act).    Yes  x    No  ¨.

The aggregate market value of the outstanding common stock, other than shares held by persons who may be deemed affiliates of the registrant, as of the last business day of the registrant’s most recently completed second fiscal quarter was approximately $29 billion. As of February 11, 2005, there were 871,519,916 shares of common stock, par value $1.00 per share, of the registrant outstanding.

Documents incorporated by reference.

Parts I, II and IV of this Form 10-K incorporate by reference certain information from the registrant’s 2004 Annual Report to Shareholders (Annual Report). Part III of this Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2005 Annual Meeting of Shareholders filed or to be filed pursuant to Regulation 14A (Proxy Statement).

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Note on Incorporation by Reference

In this Form 10-K, selected items of information and data are incorporated by reference to portions of the Annual Report and Proxy Statement. Any reference in this report to disclosures in the Annual Report or Proxy Statement shall constitute incorporation by reference of that specific disclosure into this Form 10-K.

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ALCOA INC.

Formed in 1888, Alcoa Inc. is a Pennsylvania corporation with its principal office in Pittsburgh, Pennsylvania. In this report, unless the context otherwise requires, Alcoa or the “company” means Alcoa Inc. and all subsidiaries consolidated for the purposes of its financial statements.

The company’s Internet address is http://www.alcoa.com. Alcoa makes available free of charge on or through its website its annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 as soon as reasonably practicable after the company electronically files such material with, or furnishes it to, the Securities and Exchange Commission (SEC). The SEC maintains an Internet site that contains these reports at http://www.sec.gov.

PART I

Item 1. Business.

Description of the Business

Information describing Alcoa’s businesses can be found in the Annual Report at the indicated pages:

Overview

Alcoa is the world’s leading producer of primary aluminum, fabricated aluminum, and alumina, and is active in all major aspects of the industry: technology, mining, refining, smelting, fabricating, and recycling. Aluminum is a commodity that is traded on the London Metal Exchange (LME) and priced daily based on market supply and demand. Aluminum and alumina represent approximately two-thirds of Alcoa’s revenues, and the price of aluminum influences the operating results of Alcoa. Nonaluminum products include precision castings,

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industrial fasteners, vinyl siding, consumer products, food service and flexible packaging products, plastic closures and electrical distribution systems for cars and trucks. Alcoa’s products are used worldwide in aircraft, automobiles, commercial transportation, packaging, consumer products, building and construction, and industrial applications.

Alcoa’s operations consist of five worldwide segments: Alumina and Chemicals, Primary Metals, Flat-Rolled Products, Engineered Products, and Packaging and Consumer. Alcoa businesses that are not reported to management as part of one of these five segments are combined and reported as “Other.”

The Alumina and Chemicals segment primarily consists of a series of affiliated operating entities referred to as Alcoa World Alumina and Chemicals (AWAC). Generally, Alcoa owns 60% and Alumina Limited (formerly WMC Limited) owns 40% of these entities. For more information on AWAC, see Exhibit Nos.10(a) through 10(e) to this report.

Alcoa Aluminio S.A. (Aluminio), an integrated aluminum producer in Brazil, is a wholly-owned subsidiary of Alcoa. Aluminio operates mining, refining, smelting and fabricated products facilities at various locations in Brazil. In August 2003, Alcoa acquired the 40.9% shareholding in Aluminio held by affiliates of Camargo Correa S.A. (collectively the “Camargo Group”). Prior to the acquisition, Alcoa had owned approximately 59% of Aluminio and the Camargo Group had been the principal minority shareholder since 1984. For more information on this acquisition, see Note F to the financial statements.

Recent Developments

In January 2005, Alcoa completed its acquisition of RUSAL’s controlling interests in two fabricating facilities in Samara and Belaya Kalitva in the Russian Federation for $257 million in cash.

In early January 2005, the company and BHP Billiton announced that they had completed the sale of their respective equity interests in Integris Metals, Inc., a metals service center company engaged in the processing and distribution of metals, to Ryerson Tull for $410 million in cash plus assumption of debt, which was approximately $234 million. Alcoa and BHP Billiton each owned 50% of Integris Metals.

In December 2004, Alcoa signed a letter of intent with Fujikura Ltd. of Japan in which Alcoa will obtain complete ownership of the Alcoa Fujikura Ltd. (AFL) automotive business based in Detroit, MI, and Fujikura will obtain complete ownership of the AFL telecommunications business, based in Nashville, TN. Alcoa and Fujikura currently hold a 51-49% respective ownership of both through the AFL joint venture. The transaction, expected to be implemented through a share exchange by Fujikura of all of its AFL shares for all shares in a new telecommunications subsidiary, including cash, is expected to be completed in the first half of 2005.

Also in December 2004, the company announced that it had sold a portion of its interest in the Juruti (Brazil) bauxite project to AWAC. In exchange for Alcoa’s interest in the Juruti project, Alumina Limited, Alcoa’s partner in AWAC, contributed $40 million to AWAC.

In October 2004, Alcoa announced a reorganization of its management structure to better align itself with global markets. Alcoa created a new global primary business to serve the aluminum and alumina markets, and a new global extruded products business. It also created an integrated North American & European business to serve the mill products markets. The rigid packaging business, with major operations in the U.S. and Australia, will be organized into a new global business group, and combined with Alcoa’s Asia operations and the global industrial foil business. These four new businesses, along with two existing global businesses serving the packaging and transportation markets, will give Alcoa a more simplified structure better suited to serve its customers.

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Bauxite Interests

Aluminum is one of the most plentiful elements in the earth’s crust. Aluminum is produced primarily from bauxite, an ore containing aluminum in the form of aluminum oxide, commonly referred to as alumina. Aluminum is made by extracting alumina from bauxite and then removing oxygen from the alumina. Alcoa processes most of the bauxite that it mines into alumina. The company obtains bauxite from reserves held by AWAC, from the company’s interests in Brazil, and under both long-term and short-term contracts and mining leases. In 2004, Alcoa consumed 31.0 million metric tons (mt) of bauxite from its own reserves, 6.9 million mt from related third parties and 2.7 million mt from unrelated third parties. Alcoa’s present sources of bauxite are sufficient to meet the forecasted requirements of its alumina refining operations for the foreseeable future. The following table provides information regarding the company’s bauxite interests:

Alcoa Active¹ Bauxite Interests

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Alumina Refining Facilities and Capacity

Alcoa is the world’s leading producer of alumina. Alcoa’s alumina refining facilities and its worldwide alumina capacity are shown in the following table:

Alumina Refining Capacity

In December 2004, AWAC and the Government of Jamaica signed an agreement in principle to expand the Jamalco alumina refinery in Clarendon, Jamaica by at least an additional 1.5 million mt per year (mtpy). The expansion will more than double the refinery’s total capacity to at least 2.8 million mtpy. In addition, AWAC ownership in the refinery will increase from 50% to 70%. The Government of Jamaica through Clarendon Alumina Production, Ltd. will continue to own the remaining 30%. A final decision to move forward on the project is expected to be made in the first half of 2005. Upon approval, it is expected that the expansion project will be completed by the end of 2007.

In November 2004, AWA LLC, Alcan Inc. and the Government of the Republic of Guinea signed a protocol for developing jointly a 1.5 million mtpy alumina refinery in Guinea, West Africa. This protocol sets out the items and framework for the alumina refinery project that will be negotiated as part of the memorandum of understanding (MOU) signed by AWA LLC and Alcan in May 2004. A detailed feasibility study for the refinery is expected to be completed by mid-2005, with construction to begin shortly thereafter. The refinery, which would be operated by Alcoa, would be expected to have an initial 1.5 million mtpy capacity, with expansion capability. Production is expected by early 2008.

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Alcoa and other joint venture owners of the Alumar refinery in São Luís, Brazil have expedited the engineering efforts and work toward securing permits for the 2 million mtpy expansion of the Alumar alumina refinery. The expansion calls for a retrofit of the existing unit and the addition of a second, state-of-the-art unit at the refinery. Upon completion, the facility’s capacity will be 3.3 million mtpy. It is expected that the project will be completed by early 2007.

In January 2003, Suralco and BHP Billiton signed an MOU with the Government of Suriname providing for (i) continuation and expansion of mining and refining activities in eastern Suriname and (ii) various exploration and other activities over the next two years relating to the feasibility of bauxite and alumina investments in western Suriname. Under the MOU, Suralco and BHP Billiton have exclusive rights in western Suriname and have committed to spend up to $8.5 million over 21-25 months to explore this opportunity, shared 55% (Alcoa) and 45% (BHP Billiton).

In 2003 Suralco broke ground on its capacity expansion at the Paranam alumina refinery in Suriname by 250,000 mtpy, an increase of approximately 13% that will bring total capacity of the plant to approximately 2.2 million mtpy. The expansion is substantially completed as of February 2005, six months ahead of schedule. Suralco and BHP Billiton have also signed an agreement extending the terms of their existing joint venture agreement on bauxite mining and alumina refining in eastern Suriname to 2025.

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Primary Aluminum Facilities and Capacity

The company’s primary aluminum smelters and their respective capacities are shown in the following table:

Alcoa Worldwide Smelting Capacity

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In 2004, Alcoa made significant progress toward restarting smelting capacity at the Wenatchee, Washington; Bécancour, Canada; and Massena and St. Lawrence, New York facilities. Once these restarts are complete, Alcoa will have 361,000 mtpy of idle capacity on a base capacity of 4,004,000 mtpy.

In January 2005, Alcoa and the Government of the Republic of Ghana announced that they signed an MOU to evaluate the development an integrated aluminum industry in Ghana that would include bauxite mining, alumina refining, aluminum production and rail transportation infrastructure upgrades. Alcoa will now work with the Government to conduct expedited feasibility studies, including a study on the creation of an alumina refinery with an initial capacity of up to 1.5 million mtpy. These studies are expected to be completed in 2006, at which time the parties would negotiate definitive agreements on mining, refining, smelting, rail upgrades and ownership structure, as well as total investment costs. The MOU also calls for the initial restart of three of the five existing potlines, representing 120,000 mtpy, at the Tema, Ghana smelter owned by Volta Aluminum Company Limited (Valco). Valco is owned 90% by the Government of the Republic of Ghana and 10% by Alcoa’s subsidiary, Reynolds Metals Company. The smelter, which is currently idled, will be restarted as soon as practical under an interim power rate agreement with the Volta River Authority, with alumina supply arranged by Alcoa.

In November 2004, Alcoa announced that it will invest approximately $284 million to build a new anode plant in Mosjøen, Norway. The facility, which will be built together with Elkem ASA, will produce anodes for Alcoa’s Fjardaál, Iceland and Elkem Aluminium ANS’ Mosjøen, Norway smelters. Construction of the anode plant, which is contingent on government approvals, is expected to be completed by 2007.

In October 2004, Alcoa announced that the 2003 MOU between it and the Government of the Kingdom of Bahrain was no longer in force. Under the terms of that MOU, Alcoa would have acquired a 26% stake in Alba, a Bahrain company that owns and operates an aluminum smelter with 512,000 mtpy of capacity. The company and the Government were unable to reach mutually acceptable terms to finalize the terms of the MOU.

In September 2004, Alcoa announced the start of an environmental impact assessment under terms of reference established by the Trinidad and Tobago Environmental Authority for a potential aluminum smelter in southwest Trinidad. This followed the signing in May 2004 by Alcoa and the Government of the Republic of Trinidad and Tobago of an MOU for a state-of-the-art, low emission smelter with a capacity of at least 250,000 mtpy. The MOU calls for Alcoa to take at least a 60% ownership stake in the smelter, with a Government state enterprise having responsibility for the remainder. Alcoa will take a lead role in the management and operation of the smelter and will have a right to 60% of the metal produced, with the Government state enterprise having a right to the remaining 40%, but with the commitment to make this metal available to downstream investors, including Alcoa.

In July 2004, Alcoa broke ground on its new 322,000 mtpy Fjardaál aluminum smelter in East Iceland. Bechtel Group, Inc. and its partner, HRV, an Icelandic engineering consortium, will manage the smelter construction. The smelter is scheduled to begin production in the spring of 2007. In January 2005, an Icelandic district court found, in part, in favor of a plaintiff who was challenging the Icelandic Planning Agency’s procedures in performing the environmental assessment which resulted in an Environmental Operating Permit being issued to the Fjardaál smelter. The case has been appealed to the Icelandic Supreme Court by both sides. The actual impact of the decision is unknown at this time.

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In July 2004, Alcoa announced that Aluminio would expand capacity at its share of the São Luís (Alumar) aluminum smelter by 30% or 63,000 mtpy, bringing Aluminio’s share of smelting capacity there to 262,000 mtpy. When complete, Alcoa’s share of output from the overall smelter will grow from 54 to 60%. Construction of the expansion began in the fourth quarter of 2004, with production expected to begin in the fourth quarter of 2005.

In June 2004, Alcoa announced that despite good faith negotiations between the company and the Quebec Government, it could not reach an agreement that would have allowed Alcoa to implement its previously announced plan to expand and upgrade its Baie Comeau, Quebec aluminum smelter. Despite this situation, Alcoa intends to keep the smelter in operation at least until 2010, as long as environmental requirements, energy availability and market conditions will allow.

In February 2004, Alcoa sold its 10% stake in the Alscon smelter in Ikot Abasi, Nigeria to the Federal Government of Nigeria. The Alscon smelter was 70% owned by the Federal Government and 20% held by Ferrostaal AG. Only a portion of the facility has ever been operated and has been idle since mid-1999. The Bureau of Public Enterprise, an agency of the Nigerian Government, is working to privatize Alscon. In connection with the sale, the company also terminated its entitlement to purchase all aluminum produced at the smelter for export.

Alcoa also will explore the aluminum smelting and associated hydroelectric power opportunities in western Suriname. In January 2003, Suralco signed an MOU with the Government of Suriname providing for an initial 18-month exclusive period of investigation of the feasibility of smelting and associated hydroelectric power investment in western Suriname. In December 2004, the parties agreed to extend the MOU through December 31, 2005. Under the MOU Alcoa has budgeted $1.5 million - $7.5 million in expenditures over this period to assess the investment potential and, if favorable, to negotiate an investment agreement with the Government.

Alcoa owns interests in the following primary aluminum facilities that are accounted for on the equity or cost basis method. The capacity associated with these facilities is not included in Alcoa’s consolidated capacity.