1. Chapter 6: Metals & alloys Part 2
DMT125 Materials Science
Chapter 6: Metals & alloys
Part 2

2. Aluminum alloy General properties Low density (2.7 g/cm3)
Useful for transportation manufactured products
Good corrosion resistance due to tenacious oxide film that forms on its surface
Pure aluminum has low strength, but can be alloyed to 690 Mpa
Non toxic & used mainly for food containers & packaging
Good electrical properties
Low price

3. Copper alloys General properties
High electrical & thermal conductivity
Good corrosion resistance
Ease of fabrication
Medium tensile strength
Controllable annealing properties
General soldering & joining characteristics
Higher strength

4. Stainless steels Excellent corrosion resistance
Due to high chromium contents
To make stainless steels “stainless”, must have at least 12% chromium in steel
Chromium forms a surface oxide that protects the underlying iron- chromium alloy from corroding
To produce the protective oxide, the stainless steel must be exposed to oxidizing agents
4 main types:
Ferritic
Martensitic
Austenitic
Precipitation hardening

5. Stainless steels Ferritic stainless steels Contain 12 to 30 percent Cr
Structure remains mostly ferritic (BCC, alpha iron type) at normal heat treatment conditions
Relatively low in cost (do not contain nickel)
Used as general construction materials
Special corrosion & heat resistance

6. Stainless steels Martensitic stainless steels
Contains 12 to 17 percent Cr with sufficient carbon (0.15 to 1 percent)
It is called martensitic because they are capable of developing martensitic structure after an austenitizing & quenching heat treatment
Strength & hardness are optimized
Corrosion resistance relatively poor compare to ferritic & austenitic types

7. Stainless steels Austenitic stainless steels Containing
16 to 25% Cr
7 to 20% Ni
Structure remains austenitic (FCC, gamma iron type) at all normal heat treating temperatures
Presence of nickel (has FCC structure) enables FCC structure to be retained at room temperature
High formability due to their FCC crystal structure

8. Stainless steels
Better corrosion resistance than ferritic & martensitic because carbides can be retained in solid solution by rapid cooling from high temperatures

10. Stainless steels

11. Stainless steels
PCW SS304 ball valve
PCW SS304 spool piece

12. Magnesium, titanium & nickel alloys
Magnesium alloys
Light metal (density = 1.74 g/cm3)
Costs more than aluminum
Difficult to cast because in the molten state it burns in air & cover fluxes must be used during casting
Relatively low strength & poor resistance to creep, fatigue & wear
Has HCP crystal structure. Which makes deformation at room temperature difficult since only 3 major slip systems are available
Useful for aerospace applications & materials handling equipment

13. Magnesium, titanium & nickel alloys
Titanium alloys
Relatively light metal (density = 4.54 g/cm3)
High strength (676 Mpa)
Superior corrosion resistance to chemical environments
Expensive because difficult to extract in the pure state from its compound
Has HCP crystal structure (alpha) at room temperature, which transform to BCC structure (beta) at 883 deg C

14. Magnesium, titanium & nickel alloys
Exceptional resistance to corrosion & high temperature oxidation
Has FCC crystal structure which makes it highly formable
Relatively expensive
High density (8.9 g/cm3)

15. Magnesium, titanium & nickel alloys
Nickel & monel alloys
Good strength & electrical conductivity
Good corrosion resistance
Nickel with 32% copper to produce Monel 400 alloy
Relatively high strength
Weldability
Excellent corrosion resistance to many environments

16. Magnesium, titanium & nickel alloys
Nickel base superalloys
Used for gas turbine parts
Withstand high temperatures & high oxidizing conditions
Creep resistant

17. Copyright © Mr.Mohd. Azarulsani b. Md. Azidin February 2011
END
Copyright © Mr.Mohd. Azarulsani b. Md. Azidin
February 2011