5. What is the most common reason, when performing complete joint-penetration groove weld procedure qualification testing on a weld made in 6061-T6 base metal, for a transverse tension test to fail in the heataffected zone and not meet the minimum tensile strength requirements of the welding code? A — The preheat temperature was too low. B — Overheating base metal during welding C — Excessive porosity D — Base metal embrittlement from rapid cooling The answer is B. Porosity and base metal embrittlement from rapid cooling do not occur in the heat-affected zone (HAZ) of aluminum welds, and a lower or no preheat will tend to help improve the strength of the HAZ, not lower it. Overheating the base metal during welding from slow travel speeds, excessive preheating, and/or high interpass temperature is the most common reason for reducing the strength of the HAZ in the 6xxx series base metals. The higher the preheat, interpass temperature, and heat input during welding, and the longer the HAZ is held at high temperature, the greater the reduction in strength of the HAZ. It is not uncommon for test samples in this base metal to fail to meet the minimum tensile strength because of overheating the base metal during welding. 6. Does the AWS D1.2/ D1.2M:2014, Structural Welding Code — Aluminum, allow welding anodized aluminum surfaces? A — Yes, but only if it is thin-coat anodizing. B — Welding of anodized aluminum surfaces is not allowed. C — Welding on anodized aluminum is not addressed by the code. D — Only if a special gas tungsten arc welding technique is used. E — Only if the anodized thickness is less than 18 microns. The answer is B. AWS D1.2, Clause 4.12, Preparation of Base Metal, clearly states in 4.12.4 Oxides: Thick oxide, anodizing, and water stains shall be removed from the surface to be welded and surface adjacent to the weld. 7. When compared to steel, resistance spot welding of aluminum typically requires welding schedules and equipment that deliver the following: A — Lower currents but much longer weld times B — Higher currents but much lower weld times C — Alternating current only D — Direct current only E — Both A and C The answer is B. As stated in the AWS Welding Handbook, Ninth Edition, Volume 5, Part 2, Materials and Applications, Chapter 1, Aluminum and Aluminum Alloys, (page 96) Resistance Spot Welding: The procedures and equipment for spot welding aluminum are similar to those used for steel; however, the higher thermal and electrical conductivity of aluminum alloys require some variations in equipment and welding schedules. For example, the weld current must be two to three times higher, but only one-third the cycle time than that required for a comparable joint between steel sections. 8. What do the last two of the four digits in the designation of aluminum base metals 6061 and 5052 indicate? A — The 1st and 2nd modification to the original alloy, respectively B — The primary alloying element, Mg2Si and Mg, respectively C — An indication of the base alloy minimum tensile strength, 61 and 52 ksi, respectively D — They have no special significance. The answer is D. In the Aluminum Association’s Aluminum Standards and Data, Alloy and Temper Designation System for Aluminum (ANSI H35.1/ H35.1(M) 2013), Clause 2.2: In the 2xxx through 8xxx alloy groups the last two of the four digits in the designation have no special significance but serve only to identify the different aluminum alloys in the group. Only in the 1xxx group do the last two of the four digits have significance. In the 1xxx group (pure aluminum) for minimum aluminum purities of 99.00% and greater, the last two of the four digits in the designation indicate the minimum aluminum percentage. As an example, 1060 has 99.60% purity, while 1350 has 99.50% purity. DECEMBER 2016 / WELDING JOURNAL 23 For info, go to aws.org/adindex
Welding Journal | December 2016
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