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For a lead-tin alloy of composition 80 wt Sn–20 wt Pb and at 180 ∘ C (335 ∘ F), do the following: a) Determine the mass fractions the α and β phases. b) Determine the mass fractions of primary β and eutectic microconstituents.
The microstructure of a lead-tin alloy at 180°C (355°F) consists of primary β and eutectic structures. If the mass fractions of these two microconstituents are 0.57 and 0.43, respectively, determine the composition of the alloy. There are 2 steps to solve this one.
Materials and Structure. When a lead-tin alloy with the eutectic composition is cooled slowly through the eutectic temperature it develops the microstructure shown in the photograph. The material is polycrystalline, however, each crystal grain has a lamellar structure of a - and b -phases.
Lead-tin solder layers on copper leads can form copper-tin intermetallic layers; the solder alloy is then locally depleted of tin and form a lead-rich layer. The Sn-Cu intermetallics then can get exposed to oxidation, resulting in impaired solderability.
Metal-joining Processes. 17.1 Introduction. In addition to methods such as bolting and rivetting, metal parts can be joined by means of soldering, brazing and welding. In soldering and brazing a ftller material of a different composition from the metals being joined is used to effect the joint.
The melting point of tin-lead alloys is generally between 180°C to 190°C, making them easier to work with compared to other materials that require higher temperatures. These alloys have excellent wetting properties, which help in forming strong solder joints by allowing the molten solder to spread evenly over surfaces.
The Pb-Sn phase diagram is an important tool in understanding the behavior of lead-tin alloys at different temperatures and compositions. It provides valuable information about the solidification process, the formation of different phases, and the microstructure of the alloy.
