Chapter Four EXTRUDABILITY & QUENCH SENSITIVITY

Transcription

1 Chapter Four EXTRUDABILITY & QUENCH SENSITIVITY

2 Metal Response and Extrudability Mechanical Properties Data flow stress ductility temperature Localized Deformation Extrudability Testing

3 Flow Stress Data We need flow stress data for the extrusion pressure calculations How to obtain accurate flow stress data? Is there just one value representing the flow stress in extrusion? Can we utilize a laboratory test to provide us with the desired information?

4 Which Temperature Should We Consider? Billet preheat temperature Billet temperature before extrusion Deformation zone temperature Extrudate s temperature

5 We need to simulate: Stress conditions Temperature profile Temperature changes that take place Strain (extrusion ratio) Strain rate (extrudate exit speed)

6 Which lab test? Tensile Test Compression Test Torsion Test

7 Temperature Control PROCESS induction heating gas heating temperature gradient set temperature vs. billet temperature TEST furnace heating resistive heating close loop control temperature gradient working zone

8 Simulation of the Extrusion Strain in the Lab Test Localized deformation tensile test - necking compression test - friction hill torsion test - radius dependence Do we deal with the localized deformation in extrusion?

9 Localized Deformation

10 Localized Deformation

11 Mechanical Test Data Temperature Ultimate Tensile Strength (UTS) Yield Strength (YS) Area Reduction Elongation Fracture Strain Average Strain Rate Microstructure (What is a better measure of ductility?)

12 Tensile Test

13 Temperature Role (mild steel)

14 Flow Stress f k n m exp( A / T ) Where: f A k n m T

15 Mechanical Tests tensile test friction (-), shearing (-), redundant work (-) compression test friction (+), shearing (+), redundant work (+) torsion test friction (-), shearing (+), redundant work (+)

16 Workability

17 Workability W k = F[f 1 (material), f 2 (process)] Material function (f 1 ) ductility strength strain-rate dependence on ductility stress & temperature dependence on microstructure

18 Workability Process Function (f 2 ) state of stress stress distribution temperature gradient heat transfer friction conditions EXTRUDABILITY (E x ) E x = F[f 1 (material), f 2 (extrusion)]

19 Effects of Extrusion Parameters

20 Extrusion Limit Diagram

21 Extrusion Working Range

22

23 ELD - Surface Quality

24 Extrusion Speed

25 Tearing Type 1 and 2

26 Measures of Extrudability Workability Extrusion Temperature Permitted Temperature Range Extrusion Pressure Exit Speed at Constant Load Maximum Extrusion Speed Maximum Extrusion Ratio

27 Extrudability Extrudability, i.e., workability of a material under the extrusion conditions, measured by the maximum exit speed of the extrudate, is one of the most significant factors influencing efficiency of the extrusion process.

28 Ways to Improve Extrudability Better control of the deformation zone geometry Accurate selection of speed and temperature process parameters Appropriate and uniform microstructure

29 Flow Stress and Extrudability Aluminum alloys

30 [mm] Castle & Lang

31 Mondolfo, Peel & Marcantonio [mm]

32 Reiso

33 Misiolek & Zasadzinski

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35 Relative Extrudability

36 Shape Factor

37 Billet Evaluation Billet quality Uniformity, homogenity of microstructure Intermetallics; to AlFeSi phase Grain size Microstructure gradients on the billet radius Billet surface ET 04 paper: Predictive Metallographic Assessment of Extrudability and Comparative Testing of 6xxx Aluminum Alloy Billets R.M. Kelly, K.P. Wardlow, P.F. Chaveriat, S.R. Claves, W.Z. Misiolek

38 Quench Sensitivity Ability for a given alloy to obtain certain mechanical properties through quenching proceeding age hardening Factors: Slow cooling rate Large wall thickness Hollow sections Interior supports (struts) Sections containing very thin fins

39 Quench Sensitivity (cont.) High diffusivity of Mg and Si (solute elements) High solute concentrations (higher diffusion at higher temperatures) Higher number of grain boundaries and intermetallic particles serving as nucleation sites

40 Critical Quench Rate

41 TTT Diagram

42 Temperature History

43 Press Heat Treatment