Why does solder have a lower melting point than Lead or Tin. 2

[Gav1]

Also are there any other alloys that exhibit the same properties.

 

[IRstuff]

Sure, solder falls into a category of materials called eutectics. Do a websearch:

http://csmres.jmu.edu/geollab/Fichter/IgnRx/BinryEu.html

TTFN

 

[kenvlach]

You can view many binary alloy (and a few ternary) phase diagrams at

http://cyberbuzz.gatech.edu/asm_tms/phase_diagrams/

Solder alloys typically involve 2 or more of the following: Ag, Bi, Cu, In, Pb, Sn.
Present researches on solder alloys are directed toward 1) replacement of toxic Pb and 2) increased reliability (resistance toward thermal fatigue and the growth of Sn whiskers, etc.). A portion each June issue of JOM is devoted to lead-free solders, e.g.,

http://doc.tms.org/servlet/ProductCatalog?container=JOM+2003+June

You can view the abstracts for free (entire articles if you are a TMS member).

A Pb-Sn phase diagram is below:

A liquidus surface of the Ag-Cu-Sn system used in some lead-free alloys is below: