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High Integrity Magnesium Automotive Castings (HI-MAC). DOE/USAMP Funded Project Period: April 2006 to March 2010 Yuan-Dong Li, Jay Keist, and Diran Apelian Project Update December 3 rd , 2008. HI-MAC Project. Goal - PowerPoint PPT Presentation
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High Integrity Magnesium Automotive Castings (HI-MAC)
DOE/USAMP Funded
Project Period: April 2006 to March 2010
Yuan-Dong Li, Jay Keist, and Diran Apelian
Project Update
December 3rd, 2008
HI-MAC Project
Goal
Reduce vehicle weight to meet future CAFE requirements by use of light weight Mg alloys in structural components
Objective
Develop cost effective casting technologies
(existing and new) for high integrity casting of
Mg alloys for structural automotive components
Key Technical Issues Address by HI-MAC
• Lower manufacturing costs
• Improve casting quality
• Develop Infrastructure
Major Tasks
Task 1: Squeeze casting process development
Task 2: Low pressure casting process development
Task 3: Thermal treatment of Mg castings
Task 4: Microstructural control during casting
Task 5: Computer modeling and properties
Task 6: Controlled molten metal transfer and filling
Task 7: Emerging casting technologies
Task 8: Technology / commercial transfer throughout the automotive value change
Sub-Tasks: Thermal Treatment
• Evaluate fluidized bed (FB) versus conventional heat treatment of Mg alloys
• Study strengthening kinetics of Mg alloys
• Investigate step heat treatment for enhancement of mechanical performance
Project Deliverables
• Optimum heat treatment process for Mg alloysReduced cycle timeCost effectiveApplicable for high volumes
• Fundamental understanding of the strengthening kinetics for Mg alloys
• A microstructure-property correlation of Mg alloys
Status of Investigation
• Fluidized bed heat treating of Mg alloysAM60MRI-206SAZ91D
• Analysis Influence of solution time
Tensile properties Microstructural behavior
Influence of aging time and temperature Tensile properties Precipitation behavior
AM60
• Mg-Al-Mn alloy
• Exhibits excellent ductility in the as cast condition
• Typically not heat treated
Fluidized bed heat treating trialsSolution at 424°C for 2 to 10 hrsAging at 232°C for 4 hrs
AM60Microstructural Evolution
Mg17Al12 rapidly dissolves into the Mg matrix
2 hr Solution
As-Cast
10 hr Solution100 µm
AM60Aging Precipitates Mg17Al12
5 µm
50 µm
Solution424°C - 2hr
Age232°C – 3hr
AM60 Results
• Solid solution and precipitation occurred but resulted in no strengthening after agingDiscontinuous precipitation at the grain
boundariesLarge, plate like precipitates
• No improvement in mechanical properties were obtained after heat treatment
MRI-206S
• Dead Sea Magnesium Alloy• Mg-1.5%Nd-0.2%Y-0.2%Zn-0.4%Zr• Sand or PM alloy designed for high temperature
applications
Fluidized bed heat treating trialsSolution at 540°C for 30 min to 4 hrsAging at 250°C for 1 to 8 hrs
MRI-206S – Microstructural Evolution
1hr Solution
As-Cast
4hr Solution
Mg41Nd5 dissolves rapidly into the Mg matrix
50 µm
MRI-206SAging Precipitates MgxNdx
1 µm 20 µm
Scales
Solution540°C - 2hr
Age250°C – 3hr
MRI-206S Properties (T6) vs. Solution Time
• Solution
540°C• Quenching
FB – 20°C• Aging
250°C – 3.5 h
Tensile Properties Vs. Aging Time
• Solution
540°C – 2 hrs
• Quenching
FB – 20°C• Aging
250°C
Tensile Properties for Various Aging Treatments
T6a (Under)230°C – 1 hr
T6b (Peak)230°C – 4 hrs
T6c (Peak)250°C – 4hrs
T6d (Over)270°C – 4hrs
MRI-206S Results
• Mg41Nd5 dissolves rapidly at 540°C
Most secondary phases dissolved within 1 hrSome secondary phases remain and grow (MgxNdx)
• Size and shape of aging precipitates remained constant despite varying solution and aging treatments
• FractographyCleavage fracture with facets and stepsPeak aged (T6) → Some shearing along preferred
plans• Optimum FB HT → 2 hrs at 540°C, 3-4 hrs at 230°C
AZ91D
• Recommended heat treatmentSolution
415°C for 16 to 24 hr 2 hr controlled ramp from 260 to
415°C → Avoid fusion voids
Aging 168°C for 16 hr Alternate: 216°C for 6 hr
• Eutectic phase → Mg17Al12
• Al solubility in Mg12.6 wt% at 437°C1 wt% at RT
Chemistry
● 8.3-9.7% Al● 0.15% Mn min.● 0.35-1.0% Zn● < 0.10% Si● < 0.005% Fe● < 0.030% Cu● < 0.002% Ni
AZ91 Literature ReviewAging Behavior
• β-Mg17Al12 precipitates out without the appearance of G.P. zones
• Forms both continuous and discontinuous precipitates (similar to AM60)
• Low strengthening response from aging• Mechanical properties influenced by
Solid solution (Al, Zn)Aging precipitate morphologySecondary phase morphology
AZ91 Literature ReviewHeat Treatment Observations
• Cerri and Barbagallo, Mat Letters 56 (2002) 716-720 Solution at 395°C yielded similar mechanical properties as
obtained at 415°C1
Aging at 220°C for a shorter time yielded better hardness than aging at 170°C
Solution time can be significantly reduced (2 hrs)
• Celotto, Acta Mater 48 (2000) 1775-1787 Optimum aging → 10 to 20 hours at 200°C
• Wang et al. Scripta Mater 54 (2006) 903-908 Aging precipitates had minimal influence on strength properties Suggested single step heat treatment at 370°C, No Aging
Heat Treating Analysis
• Break into 4 Experiments E1: Analyze T4 properties at 370, 390, and 415°C E2: Analyze influence of aging time on properties for samples
solutioned at 390°C E3: Influence of the heating ramp to 415°C
< 3 min 2 hr (260 to 415°C)
E4: Influence of solution time at 415°C 2 hr 6 hr
• All aging conducted at 200°C• Analyze mechanical properties
Controlled Heating Ramp
• Fluidized Bed set at 260°C
• Insert samples• Increase bed
temp by 40°C every 30 min
• Final temp of 415°C
E1: Influence of Solution Temperature on T4 Properties
Notes
Solution Time
2 hours
HT Ramp
< 3 min
Quench
FB at 21°C
E2: Influence of Aging Time on T6 Properties (390°C)
Notes
Solution
2 hr @ 390°C
Ramp
< 3 min
Quench
FB at 21°C
Age Temp
200°C
E3: Influence of Ramping Time on T6 Properties (415°C)
Notes
Solution
2 hr @ 415°C
Quench
FB at 21°C
Age
8 hr @ 200°C
E4: Influence of Solution Time on T6 Properties (415°C)
Notes
Solution
415°C
Ramp
2 hr
Quench
FB at 21°C
Age
8hr @ 200°C
Optimum Treatments
E12 hrs @ 370°C
E22 hrs @ 390°C8 hrs @ 200°C
E32 hrs @ 415°C8 hrs @ 200°C
E42 hr Ramp, 6 hrs @
415°C8 hrs @ 200°C
AZ91D Results
• Properties improved slightly for samples undergoing 2 hours at 370°C
• Properties were not reduced byA rapid heating rate to solution temperature (< 3 min) Decreased solution times of 2 hrs compared to 6 hrs
• Optimum treatmentSolution at 390°C for 2 hrs
Aging at 200°C for 8 hrs
Finishing Up
• Complete investigation on strengthening kineticsAZ91D
• Conduct fluidized bed heat treating on actual parts (automotive control arm)
• Cost analysis of fluidized bed heating of magnesium parts
Fluidized Bed Heating of the Automotive Control Arm
Work holder and Control Arms
Batch fluidized bed HT system