Project 2: Overaging of Al 7075

Group 2 - MSE 527L

Objective

Experimentally perform precipitation of Aluminium alloy 7075

Determine the effect of artificial ageing on hardness of Al-7075

Determine hardness of the alloy before and after the ageing process

Observe for optimum time duration of ageing of the alloy at a particular temperature to obtain maximum strength

Compare the differences in mechanical properties, such as ductility, tensile strength, yield strength, modulus of elasticity, and strain hardening exponent at different aging times.

Aluminium 7075●Ultimate Tensile strength : 74,000 psi - 78,000 psi

●Yield strength : 63,000 psi - 69,000 psi

●Material density : 2.810 g/cubic cm

●Specific gravity : 2.81

●Melting point : 900° F

●Modulus of Elasticity Tension : 10.4

●Modulus of Elasticity Torsion : 3.8

●High strength and excellent properties at low temperatures

●Commonly used in aircraft and aerospace applications

●Hardens by precipitation heat treatment

●Electrical conductivity is 36% of copper

Rockwell Hardness Test

●Measures permanent depth of indentation produced by load on the indenter

Depending upon hardness of material indenter to be used

The test axis should be within 2-degrees of perpendicular for correct loading

We perform this test on Al-7075 samples before and after ageing to observe the change

Background

Precipitation Hardening/Age HardeningFormation of extremely small dispersed 2nd phase particles

GP Zones

Effects on strength and hardness

OveragingWhen precipitation hardening has gone too far

Background

Tensile Test

All samples were subjected to tensile test to obtain mechanical properties after the aging

From stress and strain curve obtained following properties

Yield strength (YS)

Ultimate tensile Strength (UTS)

Ductility

Young’s Modulus (E) (YM)

Strain Hardening Exponent (n)

Procedure

7075 Aluminum samples were labeled and the initial rockwell Hardness was measured (Ten samples including two reference samples)

Samples were subjected to over aging at the 320 ºF (160 ºC) for 0,12,24,36,48 hours (Two samples at each time variant were taken for data accuracy)

Rockwell Hardness and conductivity was measured after the overaging process

Samples were then subjected to tensile test to compare the mechanical properties differences due to aging process.

Hardness

Conductivity

Stress/Strain Curves

Tensile Strength

Yield Strength

Ductility

Modulus of Elasticity

Strain Hardening Exponent

Microstructure

Sample 1 100X Longitudinal

Sample 1 100X Transverse

Microstructure

Sample 3 100X Longitudinal

Sample 3 100X Transverse

Microstructure

Sample 5 100X Longitudinal

Sample 5 100X Transverse

Microstructure

Sample 9 100X Longitudinal

Sample 9 100X Transverse

Microstructure

Sample 1 500X Longitudinal

Sample 9 500X Longitudinal

Microstructure

Sample 1 500X Transverse

Sample 9 500X Transverse

APPLICATIONS:● High strength to Density ratio: Transport, Aviation, Marine, Automotive● The strength and lightweight characteristics enhances the

applications in other fields. ● Other applications: Rock climbing equipment

Bicycle components

Inline skating frames

Hang glider airframes

● The hobby grade models typically use 7075 or the 6061 for the

chassis plates.

APPLICATIONS: ● Interesting Application: Manufacturing of upper and lower receivers as

well as the extension tubes for the high quality M16 Rifles in American military.

● Desert Tactical arms, SIG sauer and French armament company use it for their precision rifles.

● Common applications: camping knife and fork sets.● Wide use in mold manufacture: High strength

low density

Thermal properties

Ability to highly polished

References1. "Heat Treatments: Introduction." Heat Treatments: Introduction. N.p., n.d. Web. 17 Apr. 2013.

<http://www.efunda.com/processes/heat_treat/introduction/heat_treatments.cfm>.

2. "Age Hardening." Bluewater Thermal Solutions. N.p., n.d. Web. 17 Apr. 2013. <http://bluewaterthermal.com/age-hardening/>.

3. T. V. Rajan, C. P. Sharma, Ashok K. Sharma. “Heat Treatment: Principles and Techniques” 15ed. New Delhi: Prentice-Hall, 2006. 336-8.

http://books.google.com/books?id=A2QG3UssqKUC&pg=PA336&lpg=PA336&dq=gp+II+zone&source=bl&ots=Gmso2xnIks&sig=dsRTDlPIE0tyo2qF4YhpUGNLIsU&hl=en&sa=X&ei=tzJ_UaSRFOLtiwKqooDgAQ&ved=0CDoQ6AEwAQ#v=onepage&q=gp%20II%20zone&f=false

4. Effect of Ageing on Microstructure and Mechanical Properties of Bulk, Cryolled and Room temperature rolled Al 7075 Alloy by Sushantha Kumar

Panigrahi, R Jayaganthan; 2011.

5. "Rockwell Hardness Test Method | Newage Testing Instruments." Rockwell Hardness Test Method | Newage Testing Instruments. N.p., n.d. Web. 29

Nov. 2015.

6. "Rockwell Hardness Testing." Rockwell Hardness Testing. N.p., n.d. Web. 29 Nov. 2015.

7. "WWW.BUEHLER.COM." An ITW Company. N.p., n.d. Web. 29 Nov. 2015.

Questions