Explain the concept of AC balance in TIG welding and how to optimize it for a given material.

• A. AC balance only affects arc stability, not cleaning or penetration.
• B. AC balance is the same as DC current direction.
• C. Balance defines the time spent in cleaning (positive) vs penetration (negative) during the AC cycle; more cleaning is used for oxide-prone materials like aluminum; adjust balance to achieve desired cleaning and penetration.
• D. AC balance has no practical effect on welding aluminum.

Answer: (C)