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Development of Fluidized Bed Heat Treatment for AM60B Advisor: Dr. Mark Plichta Project Team: Allen Hunter Josh Bero John Pomeroy Jarrod Cunnings Dave Hunt Leanne Sedar Industry Support Bruce Cox, DaimlerChrysler Eric McCarty, DaimlerChrysler Rich Jacques, SPX Contech Outline Project Focus Objectives Background Experimental Procedure Results Conclusions Problem Statement Develop a fluidized bed heat treatment process for squeeze cast AM60B magnesium automotive components which improves mechanical properties to meet safety critical standards Objectives Use a fluidized bed heat treatment process to: Increase mechanical properties Tensile strength Ductility Hardness Decrease heat treatment times compared to conventional forced air furnaces Magnesium vs. Aluminum Disadvantages of Mg Inferior mechanical properties Greater material cost Advantages of Mg Low operating Lighter material temperature (<190°C) Better damping Lower melting point Allows for longer die life High Integrity Magnesium Automotive Components (HIMAC) Improve fuel economy through weight reduction of parts Use of magnesium instead of aluminum Improve mechanical properties of magnesium Call for minimum 7% elongation for safety critical parts Most as-cast magnesium alloys don’t meet this requirement Casting Mg Die Casting Majority of automotive magnesium castings Unable to be heat treated due to blistering Squeeze Casting Slower solidification Lower turbulence Minimizes porosity Able to be heat treated Squeeze Casting Metal fills Metal ‘Squeezed’ mold over Top Die Bottom Die into mold cavity 2-3 seconds and solidifies from the top down Molten Magnesium What comprises precipitation hardening heat treatment? Solution treatment As-cast structures contain multiple phases that are detrimental to mechanical properties Solution treatment creates a single phase solid solution Age Hardening Causes fine uniformly-dispersed second phase to precipitate This results in increased mechanical properties AM60B Alloy ASTM B94-94 Component Wt. % Mg Bal Al 5.5 - 6.5 Mn 0.24 - 0.6 Zn 0.22 Max Si 0.1 Max Cu 0.01 Max Ni 0.002 Max Fe 0.005 Max Other, each 0.02 Max Al – Mg Phase Diagram S A Fluidized Bed Heat Treatment What is it? Heated air forced through granular media Media is fluidized by the air Samples are immersed inside bed Air Line Samples in wire basket placed in bed Carbon Dioxide Line Fluidized Bed Fluidized Bed Why use it? Significant reduction of time with Al alloys Similar results anticipated for Mg alloys Used for Solutionizing and Aging Solution treated samples at temperatures below eutectic temperature of 437°C Age samples at 177°C Fluidized Bed More uniform and faster heating than conventional convection furnace Sand has a higher density Heat capacity of sand is much higher than air or gas Experimental Procedure Identify Solution Treatment Parameters with ingot samples Ingot cubes were solution treated at temperatures ranging from 415°C to 440°C Volume fractions of Mg17Al12 remaining eutectic measured using point counting method Samples examined for incipient melting Heat Treatment Results Ingot samples tested at temps of 415°C, 420°C, 430°C and 440°C at times of 2, 4, 6, and 8 hours Results revealed amount of Mg17Al12 remaining Volume fraction Mg17Al12 decreases with time and temperature Solutionizing and Aging Temp of 435°C was chosen for solutionizing Below the eutectic melting temp of 437°C Above the solutionizing temp of 430°C which had good results of reducing the percentage of Mg 17Al12 Identify Aging Parameters Pre-arranged temp of 177°C Optimize strength and elongation Project Delays Squeeze cast tensile bars were intended for project Squeeze cast cell was not operational due to local fire codes Variance was obtained but not enough time remained to produce quality magnesium squeeze cast parts Low pressure permanent mold (LPPM) tensile bars were used instead Experimental Procedures LPPM tensile bars solution treated at 435°C for various times Aged at 177°C for various times Mechanical properties were measured Tensile Hardness Solution/Age Results Hardness data follows normal age hardening trend 6 Hour Solution Treatment Best elongation – 6.5% at 0 and 1 hour of aging 8 Hour Solution Treatment Best elongation – 7.5% reached at 1 hour of aging Metallography As-cast eutectic structure (20 μm SB) 8 hour solution treated (100 μm SB) 8 hour solution treated 36 hour over-aged (20 μm SB) Conclusions Prefer to have more samples/data Most bars contained oxides Tensile bars failed prematurely at oxide areas Best Heat Treatment for AM60B Solution heat treatment of 8 hours Aging of 1 hour Both hardness and elongation peaked out at this combination Questions?
"Heat Treatment of AM60B"