Gold with highest strength and can be used in stress bearing area:
Electralloy: It is the newest form of direct filling gold. It is produced by electrolytic precipitation method. Then this crystalline structure is sandwiched between two gold foils to improve the handling properties. In this, calcium (0.1%) is added to increase the hardness and strength of the gold.
Nisha Garg, Amit Garg. Textbook of Operative Dentistry.  Edition 3. Page: 374
Gold foil
Mat gold
Spherical gold
Electralloy