3xxx Series Alloys – (non-heat treatable – with ultimate tensile strength of 16 to 41 ksi) These aluminum / manganese alloys (manganese additions ranging from 0.05 to 1.8%) and are of moderate strength, have good corrosion resistance, good formability and are suited for use at elevated temperatures. One of their first uses was pots and pans, and they are the major component today for heat exchangers in vehicles and power plants. Their moderate strength, however, often precludes their consideration for structural applications. These base alloys are welded with 1xxx, 4xxx and 5xxx series filler alloys, dependent on their specific chemistry and particular application and service requirements.
4xxx Series Alloys – (heat treatable and non-heat treatable – with ultimate tensile strength of 25 to 55 ksi) These are the aluminum / silicon alloys (silicon additions ranging from 0.6 to 21.5%) and are the only series that contain both heat treatable and non-heat treatable alloys. Silicon, when added to aluminum, reduces its melting point and improves its fluidity when molten. These characteristics are desirable for filler materials used for both fusion welding and brazing. Consequently, this series of alloys is predominantly found as filler material. Silicon, independently in aluminum, is non-heat treatable; however, a number of these silicon alloys have been designed to have additions of magnesium or copper, which provides them with the ability to respond favorably to solution heat treatment. Typically, these heat treatable filler alloys are used only when a welded component is to be subjected to post weld thermal treatments.
Summary – Today’s aluminum alloys, together with their various tempers, comprise a wide and versatile range of manufacturing materials. For optimum product design and successful welding procedure development, it is important to understand the differences between the many alloys available and their various performance and weldability characteristics. When developing arc welding procedures for these different alloys, consideration must be given to the specific alloy being welded. It is often said that arc welding of aluminum is not difficult, “it’s just different”. It is an important part of understanding these differences is to become familiar with the various alloys, their characteristics, and their identification system.
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