MMET207 Exam 3

1000 Al

commercially pure aluminum (99% minimum)

2000 Al

copper

3000 Al

manganese

4000 Al

silicon

5000 Al

magnesium

6000 Al

magnesium and silicon

7000 Al

zinc

7000-F

zinc; as fabricated

4000-W

silicon; solution heat treated

3000-O

manganese; annealed

5000-H12

magnesium; 1/4 strain hardened

3000-H18

manganese

full strain harden

What Aluminum series are heat treatable?

2000, 6000, 7000

What aluminum series are not heat treatable?

1000, 3000, 4000, 5000

2000-T3

copper; furnace solution heated, quenched and COLD WORKED

6000-T4

magnesium and silicon

furnace solution heat treated, quenched and NATURALLY AGED

7000-T6

zinc

furnace solution heat treated, quenched and FURNACE AGED

What are the physical properties of aluminum compared to other metals?

lighter than all other engineering metals, high thermal and electrical conductivity, good corrosion resistance in atmospheric environment

Aluminum has how much of the conductivity of pure copper?

60%

Which has a higher conductivity per unit mass, aluminum or copper?

aluminum

How is precipitation hardening done?

temperature raised to about 800F, water quenched and then aged

What does Fe do in aluminum?

increases the strength and hardness and reduces hot-cracking in casting

What does Mn do in aluminum?

improves ductility and impact strength, castability and reduces shrinkage

What does Si do in aluminum?

increases fluidity and corrosion resistance, makes it difficult to machine

What does Mg do in aluminum?

improves strength, difficult to cast, precipitation harden

What does Zn do in aluminum?

lowers castability, prone to hot cracking and shrinkage, promotes high strength

What does Cu do in aluminum?

increases strength, can cause brittleness, improves machinability

What is the annealing process for aluminums?

done on non-heat treatables

What is the stress relieving process for aluminums?

can be done on all alloys to prevent stress corrosion cracking

What is the highest temperature heat treatment for aluminums?

precipitation/solution hardening

What is the longest heat treatment for aluminums?

aging, which is also done at the lowest temperature

What is the difference between anodizing and hard coating?

anodizing is a thinner layer and can be colored, hard coating is thicker and done for corrosion and wear resistance only

What should you keep in mind when anodizing?

corners are hard to anodize, so rounded edges are better for this

How is anodizing done?

it is set up in a corrosive cell to help aluminum oxides form

What elements can cause problems in anodizing?

copper and silicon

Which aluminum alloys are the most susceptible to stress corrosion cracking?

2000 and 7000

Which aluminum alloys are least likely to stress corrode crack?

1000, 3000, 6000

Which aluminum alloy has the best resistance to stress corrosion cracking?

6061

In what environments is pitting found in aluminum?

high salt, seawater and water in general

What affect does detergent have on aluminum?

it leads to heavy corrosion attack

Which aluminum alloys machine best?

age-hardened

What is the stiffness of aluminum compared to steel?

1/3 stiffness of steel

What is the specific stiffness of aluminum compared to steel?

its about the same

Which aluminum alloy is not so good for welding?

7000

What is the formability of aluminum alloys?

good because of their low stiffness, ideal for extrusion

Which aluminums are easiest to machine?

6000 and 7000

What is the crystal structure of austenitic stainless steel?

FCC

What is the crystal structure of ferritic stainless steel?

BCC

What is the crystal structure of martensitic stainless steel?

BCT

Which stainless steels are magnetic?

martensitic and ferritic

Which stainless steels is hardenable?

martensitic

What is the carbon/chromium content of austenitic stainless steel?

very low carbon, 16-26% Cr

What is the carbon/chromium content of martensitic stainless steel?

up to 1.2% carbon, 12-18% Cr

What is the carbon/chromium content of ferritic stainless steel?

less than 0.2% carbon, 16-20% Cr

What is sigma phase?

an undesirable high temperature phase in SS that should be avoided, decreases mechanical properties, 50%C/50%Cr

What are the physical/mechanical properties of stainless steel?

-modulus-28-29x10^6 (slightly lower than steel)
-electrical resistivity 6 times steel
-density about same as steel
-thermal conductivity half of steel

How is passivity developed?

by immersing stainless steels in an oxidizing medium to promote the development of a protective oxide film

What is sesitivity?

undesirable chromium depletion in stainless steel

How is sensitivity developed?

from heating SS at a high temperature for an extended period of time

How can sensitization be prevented?

stabilize the material, use SS with very low carbon, stay out of sensitization time/temperature

What are stabilized stainless steels?

where elements were added to prevent the loss of corrosion resistance during welding

When are stainless steels prone to corrosion?

crevice corrosion, attack in chlorides and reducing acids, stress corrosion cracking, intergranular attack when sensitized, galvanic corrosion between grains

430

ferritic

corrosion resistant to acids

430F

ferritic

sulfur added for machinability

446

ferritic

high Cr, scaling resistance, also some offshore and coastal corrosive environments, furnace parts

403

martensitic

high temperature turbine parts

416

martensitic

free machining, fasteners

420

martensitic

cutlery, surgical instruments, tools, wear

440C

martensitic

tooling, wear, highest hardness and abrasion resistance

302

austenitic

excellent for gasoline

303

austenitic

sulfur for free machining, not as good for corrosion resistance as others

304

austenitic

excellent for gasoline

304L

austenitic

extra low carbon, same as 304 when welding or stress relieving is required

316

austenitic

resists sulfuric acid in very low and high concentrations, nitric acid, gasoline, most commonly used for chemical service

316L

austenitic

same as 316 uses when welding or stress relieving is required

300 series stainless steels are

austenitic

400 series stainless steels are

martensitic or ferritic

What are the types of ferritic stainless steel?

430, 430F,446

What are the types of martensitic stainless steels?

403, 416, 420, 440C

Which cast irons can be welded?

none

Which cast irons can be machined?

all except for white cast iron because it's very brittle

What is the chemical composition of gray cast iron?

2-4% carbon with at least 1% silicon

What is the chemical composition of malleable cast iron?

2-3% carbon, 1-1.8% silicon (made from white cast iron)

What is the chemical composition of ductile cast iron?

3-4% carbon, 2-3% silicon, some nickel

What is the chemical composition of white cast iron?

2-4% carbon, 0.5-2% silicon and 0.5% manganese

What are the physical and mechanical properties of gray cast iron?

-ferromagnetic
-good damping
-good electrical resistivity
-good corrosion resistance
-good wear resistance
-poor toughness

What are gray cast irons commonly used for?

the bases to machining equipment

What are the physical and mechanical properties of malleable cast iron?

-up to 20% elongation
-stiffness similar to steel
-excellent machinability
-good wear resistance
-good compressive strength and fatigue strength

What are the physical and mechanical characteristics of ductile cast iron?

-good machinability
-good ductility
-decent corrosion resistance
-modulus ranges from 23-25x10^6

What are the physical and mechanical properties of white cast iron?

-no graphite flakes
-good hardness and wear resistance
-very brittle

How do dendrites form?

grains are formed on solidification by atoms attaching themselves to nuclei of one form or another and usually grow in a treelike form

What is a columnar structure?

a type of casting grains that grow perpendicular to the mold walls

What is segregation?

variation of chemical composition on a microscopic scale

What are some ways to ensure a good casting design?

design it so that the gates and risers are the last to solidify

feed paths should be as uniform in cross section as possible

Whats the numbering system for gray cast irons?

denoted by class number (ex. 20, 60) which is the tensile strength/1000

What is the effect of graphite flakes on strength?

the more flakes, the lower strength

What is the effect of graphite flakes on castability?

more flakes means better castability

What is the effect of graphite flakes on machining?

more flakes makes machining easier

What is the effect of graphite flakes on surface finish?

more flakes means poor surface finish

What is the effect of graphite flakes on damping vibration?

more flakes means more damping