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Quantitative evaluation of softened regions in weld heat-affected zones of 6061-T6 aluminum alloy—Characterizing of the laser beam welding process

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Abstract

In welding 6061-T6 aluminum alloy, softening caused by the dissolution of strengthening β″ (Mg2Si) precipitates occurs in heat-affected zones (HAZs). Laser beam welding is advantageous in view of narrower softened regions. The width of the softened region in a laser beam weld with a welding speed of 133 mm/s is 1/7 that of a tungsten inert gas (TIG) weld with a speed of 5 mm/s. The hardness distributions and width of softened regions in the HAZ have been quantitatively predicted to characterize the laser beam welding process. To this end, a kinetic equation describing the dissolution of age precipitates has been established and has been applied to 6061-T6 aluminum weldments. The hardness profiles and the width of softened zones have been successfully predicted in both welding processes. Prediction of the width of softened regions with varying power inputs and welding speeds reveals that a high energy density and a high welding speed in laser beam welding result in significantly narrower softened regions, in which the width is insensitive to variations in welding parameters compared to that of TIG welding.

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Abbreviations

A :

kinetic constant

a :

thermal diffusivity (m2/s)

C 0 :

constant in equation for C i (mol pct)

c 1 :

kinetic constant

C i :

concentration of solute at precipitate/matrix interface (mol pct)

C m :

concentration of solute in matrix (mol pct)

C p :

concentration of solute inside the precipitates (mol pct)

d :

plate thickness (m)

D 0 :

constant in equation for D m (m2/s)

D m :

diffusion coefficient of magnesium in aluminum (m2/s)

f :

volume fraction of strengthening β″ precipitates

f 0 :

initial volume fraction of strengthening β″ precipitates

G(X) :

arbitrary function of X

H(T) :

arbitrary function of T

HV :

hardness (VPN)

HV max :

base metal hardness after T6 artificial aging (VPN)

HV min :

matrix hardness in absence of hardening precipitates (VPN)

K 0 :

modified Bessel function of second kind and zero order

n 1 :

time exponent

P A :

arc power (W)

P L :

laser power (W)

q 0 :

net power received by weldments (W)

Q d :

activation energy for diffusion of magnesium in aluminum (J/mol)

Q s :

metastable solvus boundary enthalpy (J/mol)

R:

gas constant (8.3143 J/mol K)

r :

radial distance from heat source (m)

r 0 :

initial precipitate radius (m)

T :

temperature (K)

t :

time (s)

v :

welding speed (m/s)

X :

fraction of dissolved precipitates in matrix

x :

x-axis/welding direction (m)

y :

y-axis/transverse direction (m)

α :

absorptivity of the specimen surface to CO2 laser beam

η :

arc efficiency factor

λ :

thermal conductivity (W/m K)

ϑ :

reduced time (s)

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Author notes

  1. Hirotaka Todaka (Student, Engineer)

    Present address: the Department of Manufacturing Science, Graduate School of Engineering, Osaka University, 565-0871, Osaka, Japan

Authors and Affiliations

  1. the Department of Manufacturing Science, Graduate School of Engineering, Osaka University, 565-0871, Osaka, Japan

    Akio Hirose (Associate Professor), Nobutaka Kurosawa (Research Associate) & Kojiro F. Kobayashi (Professor)

  2. Toyota Motor Corporation, 471-0826, Nagoya, Japan

    Hirotaka Todaka (Student, Engineer)

  3. the Advanced Production Engineering. Center, Ishikawajima-Harima Heavy Industries Co., Ltd., 235-0031, Kanagawa, Japan

    Hiroto Yamaoka (Researcher)

Authors
  1. Akio Hirose
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  2. Nobutaka Kurosawa
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  3. Kojiro F. Kobayashi
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  4. Hirotaka Todaka
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  5. Hiroto Yamaoka
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Hirose, A., Kurosawa, N., Kobayashi, K.F. et al. Quantitative evaluation of softened regions in weld heat-affected zones of 6061-T6 aluminum alloy—Characterizing of the laser beam welding process. Metall Mater Trans A 30, 2115–2120 (1999). https://doi.org/10.1007/s11661-999-0022-z

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  • DOI: https://doi.org/10.1007/s11661-999-0022-z

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