Exhibit 5.1

[LETTERHEAD OF WACHTELL, LIPTON, ROSEN & KATZ]

January 31, 2014

Noranda Aluminum Holding Corporation

801 Crescent Centre Drive

Suite 600

Franklin, TN 37067

Ladies and Gentlemen:

At your request, we have examined the Registration Statement on Form S-3 (the “Registration Statement”) to be filed on the date hereof by Noranda Aluminum Holding Corporation, a Delaware corporation (the “Company”), Noranda Aluminum Acquisition Corporation, a Delaware corporation (“Aluminum”), and each of the subsidiaries listed on Schedule I hereto, each of which is organized in Delaware (the “Subsidiary Guarantors,” and together with Aluminum and the Company, the “Guarantors”) with the Securities and Exchange Commission (the “SEC”) in connection with the registration pursuant to the Securities Act of 1933, as amended (the “Securities Act”), of (a) up to $350,000,000 in aggregate offering price of securities that may be offered and sold from time to time by the Company, including (i) shares of Company common stock, par value $0.01 of the Company (the “Common Stock”); (ii) shares of Company preferred stock, par value $0.01 of the Company (the “Preferred Stock”); (iii) stock purchase contracts of the Company (the “Stock Purchase Contracts”) which may be issued under one or more stock purchase contract agreements (each, a “Stock Purchase Contract Agreement”) to be entered into between the Company and the stock purchase contract agent to be named therein; (iv) warrants of the Company (the “Warrants”), which may be issued pursuant to a warrant agreement (the “Warrant Agreement”) between the Company and the warrant agent to be named therein; (v) debt securities of the Company or Aluminum (the “Debt Securities”) and (vi) guarantees of debt securities issued by the Company or Aluminum (the “Guarantees,” and collectively with the Common Stock, Preferred Stock, Stock Purchase Contracts and Warrants and Debt Securities, the “Securities”), which may be issued pursuant to a debt indenture (the “Indenture”) among the Company or Aluminum, as issuer, the applicable Guarantors and a trustee to be named therein; and (b) up to 33,325,673 shares of Company Common Stock (the “Selling Stockholders Shares”) which may be offered and sold from time to time by the selling stockholders named therein.

We have examined and relied on originals or copies certified or otherwise identified to our satisfaction of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary or appropriate for the purposes of this opinion letter. In such examination, we have assumed (a) the authenticity of original documents and the genuineness of all signatures; (b) the conformity to the originals of all documents submitted to us as copies; (c) the truth, accuracy and completeness of the information, representations and warranties contained in the records, documents, instruments and certificates we have reviewed; (d) the Registration Statement, and any amendments thereto (including post-effective amendments), will have become effective under the Securities Act; (e) a prospectus supplement will have been filed with the SEC describing the Securities offered thereby; (f) all Securities will be issued and sold in compliance with applicable federal and state securities laws and in the

manner stated in the Registration Statement and the applicable prospectus supplement; (g) a definitive purchase, underwriting or similar agreement with respect to any Securities offered will have been duly authorized and validly executed and delivered by the Company and the other parties thereto; (h) any Debt Securities and Guarantees that may be issued will be issued in a form that complies with the Indenture and the Indenture and any supplemental indenture to be entered into in connection with the issuance of such Debt Securities will be manually signed or countersigned, as the case may be, by duly authorized officers of the trustee named therein; and (i) any Securities issuable upon conversion, exchange, redemption or exercise of any Securities being offered will be duly authorized, created and, if appropriate, reserved for issuance upon such conversion, exchange, redemption or exercise. We have assumed that the terms of the Securities will have been established so as not to, and that the execution and delivery by the parties thereto and the performance of such parties’ obligations under, the Securities will not, violate, conflict with or constitute a default under (i) any agreement or instrument to which the parties thereto are subject, (ii) any law, rule or regulation to which the parties thereto are subject, (iii) any judicial or regulatory order or decree of any governmental authority or (iv) any consent, approval, license, authorization or validation of, or filing, recording or registration with any governmental authority. As to any facts material to the opinions expressed herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Company and others.

We are members of the Bar of the State of New York, and we have not considered, and we express no opinion as to, the laws of any jurisdiction other than the laws of the State of New York, the General Corporation Law of the State of Delaware and the Delaware Limited Liability Company Act and the federal securities laws of the United States of America, in each case as in effect on the date hereof.

Based upon the foregoing, and subject to the qualifications set forth in this letter, we advise you that, in our opinion:

1. With respect to any shares of Common Stock to be offered by the Company pursuant to the Registration Statement (the “Offered Common Shares”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Securities Act, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Common Shares has been prepared, delivered and filed in compliance with the Act and the applicable rules and regulations thereunder, (c) if the Offered Common Shares are to be sold pursuant to a firm commitment underwritten offering, the underwriting agreement with respect to the Offered Common Shares has been duly authorized, executed and delivered by the Company and the other parties thereto, (d) the Board of Directors of the Company (the “Board”), including any appropriate committee appointed thereby, and appropriate officers of the Company have taken all necessary corporate action to approve the issuance of the Offered Common Shares, the consideration to be received therefor and related matters, (e) the terms of the issuance and sale of the Offered Common Shares have been duly established in conformity with the organizational documents of the Company, do not violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company and (f) certificates in the form required under the Delaware General Corporation Law representing the Offered Common Shares

are duly executed, countersigned, registered and delivered upon payment of the agreed upon consideration therefor, the Offered Common Shares (including any shares of Common Stock duly issued upon conversion, exchange or exercise of any Warrants, Debt Securities or Preferred Stock registered on the Registration Statement), when issued and sold in accordance with the applicable underwriting agreement with respect to the Offered Common Shares or any other duly authorized, executed and delivered valid and binding purchase or agency agreement, will be legally issued, fully paid and nonassessable.

2. With respect to the shares of any series of Preferred Stock to be offered by the Company pursuant to the Registration Statement (the “Offered Preferred Shares”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Act, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Preferred Shares has been prepared, delivered and filed in compliance with the Act and the applicable rules and regulations thereunder, (c) if the Offered Preferred Shares are to be sold pursuant to a firm commitment underwritten offering, the underwriting agreement with respect to the Offered Preferred Shares has been duly authorized, executed and delivered by the Company and the other parties thereto, (d) the Board, including any appropriate committee appointed thereby, and appropriate officers of the Company have taken all necessary corporate action to approve the issuance, terms and sale of the Offered Preferred Shares, the consideration to be received therefor and related matters, (e) a Certificate of Designation conforming to the Delaware General Corporation Law regarding such series of Preferred Stock has been filed with the Secretary of State of the State of Delaware, (f) the terms of the Offered Preferred Shares and of their issuance and sale have been duly established in conformity with the terms of the particular series as established by the Board, so as not to violate any applicable law, the organizational documents of the Company or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, and (g) certificates in the form required under the Delaware General Corporation Law representing the Offered Preferred Shares are duly executed, countersigned, registered and delivered upon payment of the agreed-upon consideration therefor, the Offered Preferred Shares (including any shares of Preferred Stock duly issued upon conversion, exchange or exercise of any Warrants, Debt Securities or Preferred Stock), when issued or sold in accordance with the applicable underwriting agreement or any other duly authorized, executed and delivered valid and binding purchase or agency agreement, will be legally issued, fully paid and nonassessable.

3. With respect to any Stock Purchase Contracts to be offered by the Company pursuant to the Registration Statement (the “Offered Purchase Contracts”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Act, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Purchase Contracts has been prepared, delivered and filed in compliance with the Securities Act and the applicable rules and regulations thereunder, (c) the Board, including any appropriate committee appointed thereby, and appropriate officers of the Company have taken all necessary corporate action to approve the issuance of the Offered Purchase Contracts, the consideration to be received therefor and related matters, (d) the Stock Purchase Contract Agreement has been duly authorized, executed and delivered by the Company and the other parties thereto, (e) the terms of the issuance and sale of the Stock Purchase Contract Agreement have been duly established in conformity with the Offered Purchase Contracts, so as

not to violate any applicable law, the organizational documents of the Company or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, and (f) the Offered Purchase Contracts have been duly executed and delivered against payment therefore, pursuant to the Stock Purchase Contract Agreement, the Offered Purchase Contracts will constitute valid and legally binding obligations of the Company.

4. With respect to any Warrants to be offered by the Company pursuant to the Registration Statement (the “Offered Warrants”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Act, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Warrants has been prepared, delivered and filed in compliance with the Act and the applicable rules and regulations thereunder, (c) the Board, including any appropriate committee appointed thereby, and appropriate officers of the Company have taken all necessary corporate action to approve the issuance of the Offered Warrants, the consideration to be received therefor and related matters, (d) the warrant agreement with respect to the Offered Warrants (the “Warrant Agreement”) has been duly authorized, executed and delivered by the Company and the other parties thereto, (e) the terms of the issuance and sale of the Offered Warrants have been duly established in conformity with the Warrant Agreement, so as not to violate any applicable law, the organizational documents of the Company or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, and (f) the Offered Warrants have been duly executed and delivered against payment therefore, pursuant to the Warrant agreement, the Offered Warrants will constitute valid and legally binding obligations of the Company.

5. With respect to any series of Debt Securities to be offered by the Company or Aluminum pursuant to the Registration Statement (the “Offered Debt Securities”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Act and the Indenture has been qualified under the Trust Indenture Act of 1939, as amended, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Debt Securities has been prepared, delivered and filed in compliance with the Act and the applicable rules and regulations thereunder, (c) if the Offered Debt Securities are to be sold pursuant to a firm commitment underwritten offering, the underwriting agreement with respect to the Offered Debt Securities has been duly authorized, executed and delivered by the Company and the other parties thereto, (d) the Board or the board of directors of Aluminum, as applicable, including any appropriate committee appointed thereby, and appropriate officers of the Company or Aluminum, as applicable, have taken all necessary corporate action to approve the issuance and terms of the Offered Debt Securities and related matters, (e) the Indenture and any supplemental indenture in respect of such Offered Debt Securities have been duly executed and delivered by each party thereto, (f) the terms of the Offered Debt Securities and of their issuance and sale have been duly established in conformity with the Indentures and any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities, so as not to violate any applicable law, the organizational documents of the Company or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, and (g) the Offered Debt Securities have been

issued in a form that complies with, and have been duly executed and authenticated in accordance with, the provisions of the Indentures and any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities and duly delivered to the purchasers thereof upon payment of the agreed-upon consideration therefor, the Offered Debt Securities (including any Debt Securities duly issued upon conversion, exchange or exercise of any Warrants, Debt Securities or Preferred Stock), when issued and sold in accordance with the Indentures, any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities and the applicable underwriting agreement, if any, or any other duly authorized, executed and delivered valid and binding purchase or agency agreement, will be valid and binding obligations of the Company, enforceable against the Company in accordance with their respective terms.

6. With respect to any guarantee by any of the Guarantors with respect to a series of Offered Debt Securities issued pursuant to the Registration Statement (collectively, the “Offered Guarantees”), when (a) the Registration Statement, as finally amended (including all necessary post-effective amendments), has become effective under the Act and the Indenture has been qualified under the Trust Indenture Act of 1939, as amended, (b) an appropriate prospectus supplement or term sheet with respect to the Offered Debt Securities has been prepared, delivered and filed in compliance with the Act and the applicable rules and regulations thereunder, (c) if the Offered Debt Securities are to be sold pursuant to a firm commitment underwritten offering, the underwriting agreement with respect to the Offered Debt Securities has been duly authorized, executed and delivered by the Company and the other parties thereto, (d) the Board and/or the board or other applicable body of each applicable Guarantor, including any appropriate committee appointed thereby, and appropriate officers of the Company and/or each Guarantor, as applicable, have taken all necessary corporate action to approve the issuance and terms of the Offered Debt Securities, including the Offered Guarantees, and related matters, (e) the Indenture and any supplemental indenture in respect of such Offered Debt Securities, including the Offered Guarantees, have been duly executed and delivered by each party thereto, (f) the terms of the Offered Debt Securities, including the Offered Guarantees, and of their issuance and sale have been duly established in conformity with the Indentures and any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities, so as not to violate any applicable law, the organizational documents of the Company or of any Guarantor or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, and (g) the Offered Debt Securities have been issued in a form that complies with, and have been duly executed and authenticated in accordance with, the provisions of the Indentures and any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities, including such Offered Guarantees and duly delivered to the purchasers thereof upon payment of the agreed-upon consideration therefor, each Offered Guarantee, when issued and sold in accordance with the Indentures, any supplemental indenture to be entered into in connection with the issuance of such Offered Debt Securities, including such Offered Guarantee, and the applicable underwriting agreement, if any, or any other duly authorized, executed and delivered valid and binding purchase or agency agreement, will be a valid and binding obligation of the applicable Guarantor, enforceable against the applicable Guarantor in accordance with its respective terms.

7. The Selling Stockholders Shares are legally issued, fully paid and nonassessable.

The opinions set forth above are subject to the effects of (a) bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting the enforcement of creditors’ rights generally, (b) general equitable principles (whether considered in a proceeding in equity or at law), (c) an implied covenant of good faith and fair dealing, (d) provisions of law that require that a judgment for money damages rendered by a court in the United States be expressed only in United States dollars, (e) limitations by any governmental authority that limit, delay or prohibit the making of payments outside the United States and (f) generally applicable laws that (i) provide for the enforcement of oral waivers or modifications where a material change of position in reliance thereon has occurred or provide that a course of performance may operate as a waiver, (ii) limit the availability of a remedy under certain circumstances where another remedy has been elected, (iii) limit the enforceability of provisions releasing, exculpating or exempting a party from, or requiring indemnification of a party for, liability for its own action or inaction, to the extent the action or inaction involves gross negligence, recklessness, willful misconduct or unlawful conduct, (iv) may, where less than all of a contract may be unenforceable, limit the enforceability of the balance of the contract to circumstances in which the unenforceable portion is not an essential part of the agreed exchange, (v) may limit the enforceability of provisions providing for compounded interest, imposing increased interest rates or late payment charges upon delinquency in payment or default or providing for liquidated damages or for premiums upon acceleration or (vi) limit the waiver of rights under usury laws.

We express no opinion as to whether, or the extent to which, the laws of any particular jurisdiction apply to the subject matter hereof, including, without limitation, the enforceability of the governing law provision contained in any Securities and their governing documents.

This opinion letter speaks only as of its date and is delivered in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act. We hereby consent to the filing of copies of this opinion letter as an exhibit to the Registration Statement and to the use of our name in the prospectus forming a part of the Registration Statement under the caption “Legal Matters.” In giving this consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Act and the rules and regulations thereunder.

Very truly yours,

/s/ Wachtell, Lipton, Rosen & Katz

Schedule I: Subsidiary Guarantors

Noranda Intermediate Holding Corporation

Noranda Aluminum, Inc.

Norandal USA, Inc.

Gramercy Alumina Holdings Inc.

Gramercy Alumina Holdings II, Inc.

Noranda Alumina LLC