HEAT

TREA

TMEN

T OF

NON

FERROUS

AL U

MI N

UM

AL L O

YS

Prepared by: Abdelaziz Abdel-Moneim & Osama Bahaa

Presented to: Dr Nahed El-Mahalawy

CONTENT

• Introduction

• Why Heat Treatment in Manufacturing

• Heat Treatment of non-ferrous metals

• Heat Treatment of an Al-Cu Alloy

NON FERROUS HEAT TREATMENT

Various heating and cooling processes performed to effect structural changes in a material, which in turn affect its mechanical properties

In heat treatment, the microstructures of materials are modified. The resulting phase transformation influences mechanical properties like:

Strength Ductility Toughness Hardness Wear resistance.

WHY HEAT TREATMENT IN MANUFACTURING?Heat treatment operations are performed on metal work pieces

at various times during their manufacturing sequence

1. To soften a metal for forming before shaping2. To relieve strain hardening that occurs during forming to

prepare the material for improved manufacturability3. To strengthen and harden the metal near the end of the

manufacturing sequence to increase service life of a product

STEPS OF HEAT TREATMENT:

Heat treating is accomplished in three major stages:

• Stage l — Heating the metal slowly to ensure a uniform temperature

• Stage 2 — Soaking (holding) the metal at a given temperature for a given time and cooling the metal to room temperature

• Stage 3 — Cooling the metal to room temperature

CoolingSoaking

Heating -

HEAT TREATMENT THEORY:

• The various types of heat-treating processes are similar because they all involve the heating and cooling of metals; they differ in the heating temperatures and the cooling rates used and the final results.

• Successful heat treatment requires close control over all factors affecting the heating and cooling of a metal.

• The furnace must be of the proper size and type and controlled, so the temperatures are kept within the prescribed limits for each operation.

BASIC HEAT TREATMENT STEPS:

• The primary objective in the heating stage is to maintain uniform temperatures.

(Uniform temperatures are attained by slow heating)

• Many alloys change structure when they are heated to specific temperatures.

The structure of an alloy at room temperature can be either a mechanical mixture, a solid solution, or a combination solid solution and mechanical mixture.

A metal in the form of a mechanical mixture at room temperature often goes into a solid solution or a partial solution when it is heated

Solid solution The separate elements forming the metal cannot be identified even

under a microscope. When an alloy is in the form of a solid solution, the elements and

compounds forming the metal are absorbed into each other in much the same way that salt is dissolved in a glass of water.

BASIC HEAT TREATMENT STEPS:

Soaking Once a metal part has been heated to the temperature at which

desired changes in its structure will take place, it must remain at that temperature until the entire part has been evenly heated throughout.

The more mass the part has, the longer it must be soaked.

Cooling After the part has been properly soaked, the third step is to cool it. The structure may change from one chemical composition to another,

it may stay the same, or it may revert to its original form.

BASIC HEAT TREATMENT STEPS:

HEAT TREATMENT FOR NON FERROUS

Non ferrous metals requires different phases of transformation than

Those of the ferrous metals.

Three main types of heat-treating operations can be performed on nonferrous metals. I. Annealing II. Solution heat treating.III. Precipitation Hardening

ANNEALING

• annealing is the opposite of hardening, You anneal metals to relieve internal stresses, soften them, make them more ductile, and refine their grain structures.

• Annealing consists of heating a metal to a specific temperature, holding it at that temperature for a set length of time, and then cooling the metal to room temperature.

• The cooling method depends on the metal and the properties desired.

• Functions of Annealing:

1. Reduce hardness and brittleness of metal after cold working

2. Soften metals to improve machinability or formability

3. Recrystallize cold worked metals

ANNEALING

• When a cold worked metal is heat treated to revert it back to the properties and structure prior to cold work.

• The process entails three stages: 1. Recovery2. Recrystallization3. Grain growth.

ANNEALING TO REDUCE WORK HARDENING• Cold worked parts are often annealed to reduce strain

hardening and increase ductility.

• When annealing is performed to allow for further cold working of the part, it is called process annealing.

• When no subsequent deformation will be accomplished, it is simply called annealing.

PRECIPITATION HARDENING

• Precipitation hardening is commonly used to process aluminum alloys and other non-ferrous metals for commercial use.

• Examples: aluminum – copper, copper – tin , Magnesium – Aluminum and some ferrous alloys also.

• The strength and hardness of some metal alloys may be enhanced by the formation of extremely small uniformly dispersed particles of a second phase within the original phase matrix.

• This is accomplished by appropriate heat treatment.

• The process is called precipitation hardening because the small particles of the new phase are termed precipitates.

MECHANISM OF HARDENING

• During plastic deformation:

I. Zones or precipitates acts as obstacles to dislocation motion.

II. Stress must be increased to push the dislocation through distribution of precipitates.

III. Consequently the alloys becomes harder and stronger

precipitates form because the solid solubility of one element (one component of the alloy) in the other is exceeded.

PRECIPITATION HARDENING PROCESS• Solution treatment in which

the alloy is heated to a temperature above the solvus line into the alpha phase are held for a period sufficient to dissolve the beta phase.

• Quenching to room temperature to create a super saturated solid solution.

• Preciptation treatment; alloy is heated to temperature below Ts to cause precipitation of fine particles of beta phase

Single phase

2 Phases

• A composition that can be precipitation hardened contains two phases at room temperature but can be heated to a temperature that dissolves second phase

PRECIPITATION HARDENING PROCESS

PRECIPITATION HARDENING MECHANISM

• The materials in the alloy are allowed to precipitate out of the solid solution, One element (solute) atoms diffuse to nucleation sites and combine the other element (solvent) atoms

• This process occurs under controlled conditions so that the resultant grain structure will produce a greater tensile strength in the metal than in its original condition.

PRECIPITATION HARDENING

• An illustration to the process occurs during heat treatment:

AGE HARDENING REQUIREMENTS:

Four conditions must be satisfied for an alloy to have an age-hardened response during heat treatment:

1. the alloy must form a single phase on heating above the solvus line, then enter a two-phase region on cooling

2. matrix should be relatively soft and ductile, and the precipitate should be hard and brittle.

3. The alloy must be quenchable.

4. A coherent precipitate must form

HEAT TREATMENT FOR NON FERROUS ALLOYS• Aluminum alloys can be obtained in various conditions of heat

treatment called temper designations refers to aging or hardening that has been brought about by cold working the alloy. “Stabilizing” refers to a particular aging process that freezes or stops the internal changes that normally would take place in the alloy at room temperature.

• Magnesium alloys can be subjected to all of the nonferrous heat treatments, but the different alloys within the series require different temperatures and times for the various processes.

• Copper alloys are generally hardened by annealing.

• The nickel alloys can also be annealed and certain types can be hardened by heat treatment. Likewise,

• titanium may be annealed (mostly relieve machining or cold-working stresses) but is not noticeably affected by heat treatment.

TYPICAL PRECIPITATION HARDENED ALLOYS:• Al 2014 forged Air craft fittings.

• Al structures 2024 high strength forgings.

• Olympic bikes Cu

• Bronze: surgical instruments.

AL-CU ALLOY

AL–CU ALLOY

• For an alloy with the composition 95.5% Al-4.5% Cu, a single-phase (α phase) substitution solid solution of copper (solute) in aluminum (solvent) exists between 500° and 570°C.

• This alloy can be heat treated, in 3 steps:

1. Solution treatment.

2. Quenching.

3. Age hardening

Example of age hardening 2XXX series aluminum alloy system

SOLUTION TREATMENT:

• In solution treatment, the alloy is heated to within the solid-solution α phase -say, 54O°C- and then cooled rapidly by quenching it in water.

• The structure obtained soon after quenching consists only of the single phase supersaturated α solid solution; this alloy has moderate strength and considerable ductility.

QUENCHING & PRECIPITATION:

• In this process, the alloy is reheated to an intermediate temperature and then held there for a period of time, during which precipitation takes place.

• The copper atoms diffuse to nucleation sites and combine with aluminum atoms; this process produces the theta phase, which forms as submicroscopic precipitates.

A new structure (B) is stronger and less ductile than that in A

Is formed.

The increase in strength is due to increased resistance

to dislocation movement in the region of the precipitates.

• In the precipitation process, if the reheated alloy is held at the elevated temperature for an extended period of time, the precipitates begin to merge and grow. They become larger, but fewer, this process is called over aging.

• Strength reaches the peak value and then decreases .

• The resulting alloy is softer and weaker.

AGING

The yield strength hardens by the formation of precipitates, which after longer times (get large) and the strength falls off. The strength does not fall off at low aging temperatures.

Ageing & Over Aging Illustration :

REFERENCES

• ASM Metals HandBook Volume 4 - Heat Treating.

• “Precipitation Hardening” Dr. H. K. Khaira Professor in MSME MANIT, Bhopal.

• “Understanding Aluminum Heat Treatment,” Industrial Heating, February 2006