Metallurgy for Dummies

Precipitation Hardening Overview

Precipitation hardening also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys ofaluminium, magnesium, nickel, titanium, and some stainless steels. Precipitation hardening relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the movement of dislocations, or defects in a crystal’s lattice. Unlike ordinary tempering, alloys must be kept at elevated temperature for hours to allow precipitation to take place. This time delay is called aging.

Note that two different heat treatments involving precipitates can alter the strength of a material: solution heat treating and precipitation heat treating. Solid solution strengtheninginvolves formation of a single-phase solid solution via quenching. Precipitation heat treating involves the addition of impurity particles to increase a material’s strength. Precipitation hardening via precipitation heat treatment is the main topic of discussion in this article.

(continue reading…)

You might also like

Heat Treatment Furnaces Heat Treatment Furnaces of Steel Heat treating...

Optimal Combination of STRENGTH and TOUGHNESS Optimal Combination of STRENGTH and TOUGHNESS Preceding...

Aluminum “Hardening” – How it works? Heat Treatment of Aluminum The term “heat...

Do you know Heat Treatment process ? Heat Treatment Heat Treatment is the controlled...

For most uses of gold the pure metal is too soft on its own and is therefore hardened by the addition of alloying elements, copper, silver, nickel, palladium and zinc. Gold is of course yellow and the various colours seen such as red, white and green are simply alloys of gold. The final colour is dependent on the ratios and type of alloys added.

Gold Alloys

Pure gold is weak, having a tensile strength of less than 20,000psi (138 megapascals) when annealed; however, by alloying with copper, sometimes in conjunction with silver or nickel, and often a little zinc, gold alloys with strengths of 60,000–100,000 psi (414–690 MPa) may be made. Addition of these metals changes the color of gold so that red, yellow, greenish, and white golds result. The proportion of gold in solid gold jewelry is designated in karats (k); pure gold is 24 k, 18 k is 18/24 or 75% pure gold, and 14 k is 14/24 or 58.3% pure gold.

(continue reading…)

You might also like

What is Gold? Gold the Metal Non-Ferrous Gold is a chemical...

Gold Plating Gold Electroplating - How it works ? Gold...

How does gold corrode? Gold Corrosion - How it works ? Gold is...

Gold Mine Gold Mine Gold artifacts found at the Nahal...

Gold Mine

Gold artifacts found at the Nahal Kana cave cemetery dated during the 1980s, showed these to be from within the Chalcolithic, and considered the earliest find from the Levant (Gopher et al. 1990). Gold artifacts in the Balkans also appear from the 4th millennium BC, such as those found in the Varna Necropolis near Lake Varna in Bulgaria, thought by one source (La Niece 2009) to be the earliest “well-dated” find of gold artifacts. Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.

Gold is the most malleable and ductile of all metals

Chemically, gold is a transition metal and a group 11 element. Less commonly, it occurs in minerals as gold compounds, usually with tellurium. Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold dissolves in mercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test.

(continue reading…)

You might also like

Gold Alloys For most uses of gold the pure metal is too...

How does gold corrode? Gold Corrosion - How it works ? Gold is...

Gold Plating Gold Electroplating - How it works ? Gold...

What is Gold? Gold the Metal Non-Ferrous Gold is a chemical...