Chapter 6 Overview - PowerPoint PPT Presentation

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Chapter 6 Overview

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Chapter 6 Overview Four major alloy groups most common: Aluminum, magnesium, zinc and ZA These alloys have a range of properties and characteristics – PowerPoint PPT presentation

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Title: Chapter 6 Overview


1
Chapter 6 Overview
  • Four major alloy groups most common
  • Aluminum, magnesium, zinc and ZA
  • These alloys have a range of properties and
    characteristics
  • Properties are slightly less but overlapping with
    sheet steels
  • Properties are greater than but somewhat
    overlapping with high strength plastic resins

2
Chapter 6 Objectives
  • Correctly identify the most common alloy from
    each major group
  • Identify the alloy with the highest strength
  • Identify the major alloying ingredients from an
    alloy specification
  • List nine important criteria used to select an
    alloy for a particular job

3
New Terms
  • Tensile strength
  • Maximum stress achieved when pulling a test
    specimen to failure in the direction of its
    length
  • Yield strength
  • Level of strength at which elastic strain becomes
    plastic strain

4
New Terms
  • Elongation
  • Amount of permanent extension in the vicinity of
    the fracture in the tension test
  • Modulus of elasticity
  • Slope of the elastic portion of the stress-strain
    curve in mechanical testing

5
Mechanical Properties
  • Properties include tensile strength (ultimate),
    yield strength, elongation (ductility), and
    modulus of elasticity (MOE)
  • Predicts how alloy will react to stressed
    condition
  • Strong alloy high values of tensile and yield
    strengths and MOE, and low values of elongation
  • Weak alloy low strengths and MOE, and higher
    values of elongation

6
Aluminum Alloy Characteristics
  • Has a specific gravity of 2.7 lightweight
  • As a base, it has 3 primary alloying ingredients
    silicon, copper and magnesium
  • All the other ingredients can be called
    impurities
  • In some cases impurities must be controlled at
    specific levels, in other cases the level of
    impurity may be an economic compromise

7
Aluminum Product Applications
  • 380 aluminum alloy most commonly used
  • Lawn mower housings, electronics chassis, engine
    components, home appliances, tools
  • 383 and 384 for intricate components, improved
    die filling, improved resistance to hot cracking
  • 360 improved corrosion resistance, superior
    strength

8
Aluminum Product Applications
  • 443 greatest ductility
  • 413 excellent pressure tightness, highly fluid
    and useful for intricate detail
  • 390 greatest wear resistance
  • 518 very good corrosion resistance and
    ductility used in marine and aircraft hardware
    and also in escalators

9
Magnesium Alloy Characteristics
  • Has a specific gravity of 1.74 lightest
    commonly used structural metal
  • As a base, it has 4 primary alloying ingredients
  • Aluminum, zinc, manganese and silicon
  • All other ingredients are impurities and are
    controlled to maximum limits

10
Magnesium Product Applications
  • AZ91D found in drive train automotive components
    as well as handheld and laptop computers
  • AM60A has good elongation and toughness used in
    automotive wheels and steering wheels and archery
    equipment
  • AS41A has creep strength at elevated temperatures

11
Zinc Alloy Characteristics
  • Has a specific gravity of 7.0 one of the
    heavier commonly used structural metal
  • As a base, has 3 primary alloying ingredients
  • Aluminum, magnesium and copper
  • All other ingredients are impurities and are
    controlled to maximum limits
  • Sometimes referred to as Zamak
  • Highest purity of the die casting alloys

12
Zinc Alloy Product Applications
  • 3 zinc specified most frequently for functional
    and hardware castings
  • 5 zinc has higher tensile strength, hardness,
    creep resistance automotive locks
  • 7 zinc has slightly lower hardness and higher
    ductility higher fluidity than either 3 or 5
    could be a better choice for thinner walls and
    finer detail

13
ZA Alloy Characteristics
  • Developed in 1950s
  • Alloys of zinc, aluminum and copper
  • Superior properties over Zinc Alloys
  • Wear resistance
  • Creep resistance
  • Higher strength
  • Lighter weight

14
9 Criteria Alloy Cost
  • An important factor in overall product cost
  • Cost of alloy should be converted to a volume
    basis
  • Aluminum alloys usually have lowest cost per
    cubic inch
  • Magnesium and zinc can be competitive because can
    be cast with thinner walls and at reduced volume

15
9 Criteria Process Cost
  • An important component of overall product cost
  • Alloys run with hot chamber process usually run
    in smaller DCMs and at higher production rates
    than equivalent casting with the cold chamber
    process
  • Maintenance and replacement costs can vary
    significantly

16
9 Criteria Structural Properties
  • Aluminum alloys have the highest modulus of
    elasticity (MOE)
  • Relatively high strength/low density
  • Magnesium has lower strength and rigidity
  • Competitive with aluminum in some applications
    through strategic placement of reinforcing ribs
  • ZA alloys offer highest tensile and yield
    strengths

17
9 Criteria Minimum Weight
  • Magnesium alloys are the dominant choice if
    weight must be minimized

18
9 Criteria Impact Strength and Dent Resistance
  • Highest among the zinc (Zamak) alloys
  • Diminishes sharply as temperature is reduced
    below 32ºF (0ºC)
  • Impact resistance of aluminum and magnesium
    alloys varies within each alloy group

19
9 Criteria Surface Finish
  • Surface finish best achieved by the zinc and
    magnesium alloys
  • Die steel surface quality is essential to casting
    surface quality

20
9 Criteria Corrosion Resistance
  • Corrosion resistance varies from alloy to alloy
    and within an alloy group
  • Can be improved with low-cost surface treatments

21
9 Criteria Bearing Properties and Wear
Resistance
  • Bearing properties and wear resistance
  • Good for hydrodynamic bearing applications
  • If partial lubrication only, ZA alloys and 390
    aluminum resistant to abrasion and wear

22
9 Criteria Machineability
  • Machineability of all alloys excellent
  • Magnesium alloys offer best machinability in
    terms of tool life, energy consumption and low
    cutting forces

23
Freezing
  • Same as water
  • Various metals freeze at a particular temperature
    for that metal
  • Time versus temperature chart is slightly
    different than that for elements (pure metals)
    and compounds

24
Quality
  • Alloy chemical composition is controlled by an
    ASTM, American Society for Testing and Materials,
    specification
  • Each die casting plan has a method for
    maintaining alloy quality
  • Begins with purchasing of material, and continues
    through manufacturing process and shipment

25
Quality Cleanliness
  • Cleanliness component of alloy quality
  • Not as easily checked as chemical composition
  • Each time alloy is melted, some material is
    oxidized
  • Oxides are impurities in alloy that could affect
    the castings properties if not removed
  • Processes to minimize amount of oxidation and
    remove the oxides from the alloy

26
Summary
  • Designers consider range of issues when creating
    a die casting
  • Each alloy has different mechanical properties
    tensile strength, yield strength, elongation, and
    MOE
  • The alloy chosen must be appropriate to the die
    castings application
  • Alloy selection is based on characteristics and
    properties of the alloys in 9 categories
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