Computational design and development of a new, lightweight cast alloy for advanced cylinder

heads in high-efficiency, light-duty enginesMike J. Walker

General Motors

6/9/2016Project ID #PM061

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project start date 02/2013Project end date 09/2017Percent complete 70%

Engine Durability– Current materials limit engine efficiency

by limiting peak cylinder temperatures and pressures

– Insufficient tensile and fatigue properties beyond 150 C

Material Cost• Total project funding– DOE share $3,498,650– Contractor share $1,646,423

• Funding received in FY15– $591,931

• Funding for FY16 planned – $1,022,863

Timeline

Budget

Barriers

Partners

Overview

• Questek Innovations LLC• Northwestern University• American Foundry Society• Dr. Fred Major• Camaneo Associates• MIT• Project lead General Motors

2

Relevance- Project Objectives

Based on 1999 studyMg alloy Al alloy

DOE FOA 648-3a Material Property TargetsProperty Baseline DOE Target

Tensile Strength (ksi/MPa) 33/227 40/276Yield Strength (ksi/MPa) 24/165 30/207Elongation (%) 3.5 3.5Shear Strength (ksi/MPa) 26/179 30/207Endurance Limit (ksi/MPa) 8.5/59 11/76Fluidity (Spiral test) Excellent ExcellentHot Tearing Resistance Excellent ExcellentTensile Strength (ksi/MPa) 7.5/52

@250 C9.5/65

@300 CYield Strength (ksi/MPa) 5.0/34

@250 C6.5/45

@300 CTo meet energy efficiency targets, peak engine pressures and temperatures will greatly exceed current material properties and therefore material needs to be improved

Relevance - Project Objectives 2015-2016

VTO Lightweight materials

Increase understanding of materials through modelling and computation

Material property improvement (strength, stiffness, and/or ductility)

GM lightweight cast alloy project

Continued thermodynamic and mobility database development for three alloy concept structures

Determination of Theta/Q/Beta phase stability regions. Computational verification of wide chemical variation of the Q phase based on LEAP examination

Development of rod-based strength models based on Q phase growth kinetics

Generation of tensile data at room and high temperatures for Q, TQ based alloys

Approach/Strategy

Research to date has been to improve the high temperature strength of the precipitate phases. Future plans are to investigate dispersoid strengthening.

System design chart illustrating links among processing/structure/properties relationships

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Approach/Strategy 2015/2016

In 2016 fatigue properties of two new alloys will be generated and analyzed. Casting defects (porosity and oxides, related to alloy castability) determine ultimate fatigue properties.

8 10 12 14 16 18ln ( N f )

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

ln ln

(1/(1

-Fw)

)

Sr-modified A356-T6SDAS: 20 ~ 80 µmσa= 100MPa, R = 0.1

Pores

Oxides

Slip bands

w-hip-3.grf

m = 1.8N0 = 8.19 x 105

NFw = 0.1%= 1.759 x 104

R = 0.9711

m = 2.0N0= 5.79 x106

NFw = 0.1%= 1.71 x 105

R = 0.911

m = 1.68687N0 = 2.3158 x 105

NFw = 0.1%= 3.858 x 103

R = 0.981648

Q. Wang, et al., 2001

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Milestones 2015-2016Milestone Date

planned/completed

6. Validation of Sub-scale Concepts and Models 4/30/15 Comp.

Go/No-Go Proof of phase prediction based on Models Passed7. First Generation Alloy Designs 6/26/15 Comp.8. Lab-scale Castings of First Generation Designs 10/23/15 Comp.9. Alloy Characterizations and Validation 01/26/16 Comp.Go/No-Go Demonstration of high temperature property improvement in at least one variation of alloy

Passed

10. Final Computational Design Completed 06/16 Planned11. Lab Scale Castings Completed 09/16 PlannedGo/No-Go Demonstrate 10% property improvement over baseline alloys

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Technical AccomplishmentsValidation of Sub-Scale Concepts and Models

• Leap/TEM evaluations of Q alloy, Theta Q (TQ), and Beta (M)precipitation.

• Q phase chemistry is variable and exists at very low Cu content.

Technical AccomplishmentsFirst Generation Alloy Designs

• Six alloy designs were created for further evaluation based on the Q, TQ, M, and Theta precipitate structures.

• Alloys designed for better castability and maximized amount of precipitate phases for strength.

• Based on isothermal hardness studies, cast alloys M and Theta were rejected.

Cast Q Alloy Cast TQ Alloy

Cast M AlloyCast Theta Alloy

Technical AccomplishmentsLab-Scale Castings of First Generation Designs

DOE Target Q Alloy TQ Alloy RTA Alloy

UTS RT (MPa) 276 350 412 402YS RT (MPa) 207 286 365 341Elongation RT (%) 3.5 6 3.3 3

UTS 250C (MPa) -- 110 92 102YS 250 C (MPa) -- 89 70 79UTS 300C (MPa) 65 51 54 68YS 300C (MPa) 45 39 42 55

Fine Microstructure

For high temperature strength, the Rio Tinto Alcan (RTA) experimental alloy1. with Zr, V, and Mn are able to meet DOE high temperature targets. However ductility is insufficient. 1. Michel Garat, Fonderie Magazine 2010 no. 2. P 21-33.

Elevated temperature samples conditioned for 200 hours at temperature before testing

Technical AccomplishmentsLab-Scale Castings of First Generation Designs

DOE Target Q Alloy TQ Alloy RTA Alloy

UTS RT (MPa) 276 323 360 343YS RT (MPa) 207 279 345 313Elongation RT (%) 3.5 2.3 0.5 0.9

UTS 250C (MPa) -- 103 91 91YS 250 C (MPa) -- 80 72 68UTS 300C (MPa) 65 54 54 64YS 300C (MPa) 45 42 42 52

Coarse Microstructure

Elevated temperature samples conditioned 200 hours at temperature.Ductility of coarse microstructures is a major concern and must be adequately addressed.

Technical Accomplishments Alloy Characterization and Validation

•! Q/Theta stability and solubility validated with atom probe/TEM o! Extended thermodynamic databaseo! Partitioning of Ni and other elemental

additions to Q observed in LEAP o! Evaluated strengthening of additions

•! Eutectic Q design Validated

Precipitate Proxigram

(Ni) LEAP of Q+Ni

FCC+Si+Q+Theta (QT1218B)

FCC+Si+Q (QT1218B)

SSii 44..99--77..22 aatt..%%FFCCCC++QQ++TThheettaa++SSii

FFCCCC++QQ++SSii

FFCCCC++BB++SSii

CTQ Q: 0.66% T: 3.52%

356.2+0.75Cu Q: 0.94%

CQ Q: 1.18%

356.2 B’: 0.58%

CM Q: 0.94%

Modified QT database

Q+FCC+Theta

Q+FCC

Eutectic Q Alloy Design and Validation

Elemental Addition Hardness

Mg2Si

Technical AccomplishmentsStrength Model Development

Yield strength predictions versus experiment for Q-phase strengthened alloys

• Precipitate growth models validated and extended for strength model application• Rod-based strength models developed for precipitation strengthening• Strength models allow parametric design of alloys with maximized strength:

New alloy concepts generatedQ-phase Evolution (LEAP) High-Q alloy Designs

Q phase fraction modification

Solution Window Design

Responses to Reviewers CommentsQuestion 1. Approach to performing the workReviewer: Thermal conductivity needs to come in a more systematic way and there is a need for better tools for thermal conductivity?Response: We have identified models for thermal conductivity in aluminum, but we are waiting on

optimizing other properties before focusing on this aspect.Reviewer: Minor changes to existing chemistry of known precipitates will not achieve a wholesale increase in strength properties. Suggests a more transformation approach would need to be evaluated to achieve success?Response: We have investigated a number of novel concepts with transformative precipitate

strengthening phases using high-throughput DFT methods (OQMD searches for lattice matched structures). These searches found new precipitates including Al12X (X=Mo, W, etc.), and Ti and Cr structures. However, sub-scale alloys did not show clear phase formation of the targeted phases, so this avenue of search was abandoned.

Given the high temperature stability and strengthening properties of the Q-phase, we focused on the refined characterization and optimization of a Q-phase strengthened alloy. We expanded databases that incorporated the solubility of Cu in the Q-phase and strength models that involved rod-shaped precipitate strengthening. These models have now been used in the new design of higher-strength (and phase fraction) Q-phase alloys that are currently being examined.

Reviewer: What is the mechanism for using the developed information to improve the predictive models?Response: We expanded both strength and thermodynamic models to predict Q-phase and Theta-

phase strengthening.

Responses to Reviewers CommentsQuestion 2: Technical Accomplishments and Progress towards Goals

Reviewer: TEM micrographs at different scales/orientations were not sufficient and that DFT calculations should have covered a much wider composition range.

Response: We did perform high-throughput DFT analysis of hundreds of thousands of crystal structures. These possible precipitates were analyzed for lattice matching, solubility in aluminum, and phase stability with FCC aluminum. In addition we performed targeted calculations of elemental segregation and interfacial strengthening of elements with the Q-phase. In experimental trials, we did confirm elemental segregation of a subset of these elements, but we were unable to show significant properties changes due to the low solubility of these elements in aluminum.

Reviewer: Modelling effort appears to be focused on single material characteristics which can result in sub-optimization and strength versus ductility tradeoff not adequately predicted from the modelling efforts.

Response: We continue to evaluate strength, ductility, and other key properties, but the primary focus at this point has been the characterization of the precipitate phases. We are concurrently performing phase field modeling to further understand eutectic solidification modifications with minor elements. However, building a strengthening model requires a more thorough understanding of precipitate stability, growth, and coarsening, and thus, we have focused on this property before we move onto other properties predictions.

Collaboration and CoordinationGeneral Motors – Principle Investigator

– Project administration, casting simulation, casting experiments, mechanical properties, microstructural evaluation, castability evaluation

QuesTek Innovations LLC – Industrial sub-partner– Industrial Sub-partner – ICME calculations – thermodynamics, kinetics, DFT alloy generation, alloy concept

generation, parametric and final alloy designs, heat treatment process recommendations

Northwestern University – University sub-partner– DFT alloy generation, Phase Field modelling of microstructure, experimental

validation - Optical, SEM,TEM, LEAP Fred Major, Tom Prucha (AFS),– Industrial sub-partners

– Technical advisorsCamanoe Associates – Industrial sub-partner (to begin in 2016)

– Process Based Cost ModellingMIT – University sub-partner (to begin in 2016)– Recyclability Analysis

Remaining Challenges and Barriers

The high temperature strength target has been achieved in a high copper, dispersion strengthened alloy. However ductility is limited and will not meet fatigue requirements. High Cu alloys have low thermal conductivity and thus will produce higher temperatures in the combustion chamber. The challenge is to develop an alloy with the high temperature strength, still maintain room temperature ductility and have good thermal conductivity.

Future Work 2016

• Head casting trials on two Q based alloy designs (2Q 2016)• Tensile, high cycle fatigue and low cycle fatigue testing, microstructure, porosity

and castability evaluation• Measurement and development of thermal conductivity models• Extensions of strength model to include eutectic silicon and other dispersiods• Final computational design of the alloy• Lab scale castings of the final design• Further computational development and test of high volume Q phase alloys for

increased high temperature strength

2017• Head component casting trial of final alloy design • Recyclability analysis • Alloy and component cost models• Evaluation of final material properties and validation of system models

Summary

• In 2015 four alloy concepts were validated with TEM and LEAP imaging. Thermodynamic databases were updated to better reflect the observe chemical compositions for future alloy development. Strength models based on the growth kinetics of the Q rod shape structure were implemented.

• The Q phase was selected for further development because of inherent ductility and initial high temperature strength being comparable to TQ phase.

• Additional minor elements were investigated for increased high temperature stability of the Q phase but unfortunately did not show promise.

• Investigation into dispersoid elements for high temperature strength has been initiated.