Effect of Annealing on Preliminary Treatment of Aluminum Alloy 1421 by Low-Energy Laser Pulses

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Transcript of Effect of Annealing on Preliminary Treatment of Aluminum Alloy 1421 by Low-Energy Laser Pulses

  • UDC 669.715:621.791.72

    EFFECT OF ANNEALING ON PRELIMINARY TREATMENT

    OF ALUMINUM ALLOY 1421 BY LOW-ENERGY LASER PULSES

    P. Yu. Kikin,1 A. I. Pchelintsev,1 and E. E. Rusin1

    Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 25 27, July, 2013.

    The effect of annealing on preliminary treatment of aluminum alloy 1421 by low-energy laser pulses is stu-

    died. It is shown that after annealing the action of the preliminary laser treatment on the time of the start of fu-

    sion under very intense laser treatment disappears.

    Key words: low-energy laser treatment, annealing, aluminum alloy.

    INTRODUCTION

    It is shown in [1] that preliminary low-power pulsed la-

    ser irradiation shortens the time of the start of the process of

    fusion of aluminum alloys 1421, 1570 and AMG6 in subse-

    quent laser heating with energies exceeding the fusion

    threshold. It has been established that this effect manifests it-

    self only until the moment of formation of microscopic crat-

    ers on the surface of the alloy. After the formation of micro-

    craters the time of the start of fusion increases upon growth

    in the number of pulses of preliminary laser treatment. It has

    been assumed that the effect of shortening of the time before

    the start of fusion is connected with growth in the concentra-

    tion of nonequilibrium vacancies in the surface layer of the

    material in the preliminary treatment. The disappearance of

    this effect upon formation of microcraters is caused by low-

    ering of the concentration of nonequilibrium vacancies due

    to their merging into pores, the appearance and growth of

    which results in detachment of the oxide film on the surface

    of the alloy. It should be expected that the decrease in the

    concentration of vacancies due to annealing should lead to

    suppression of the effect mentioned.

    The aim of the present work was to study the effect of

    annealing on the time of the start of fusion of aluminum alloy

    1421 preliminarily subjected to low-power laser irradiation.

    METHODS OF STUDY

    We studied test pieces of alloy 1421 (Al 5.5% Mg

    2.2% Li 0.12% Zr 0.2% Sc) with grains 10 20 m in

    size. The test pieces were irradiated by a YAG:Nd+3 pulse la-

    ser. The irradiation was performed at an energy of up to 25 J

    and a pulse length of about 8 msec.

    The preliminary irradiation consisted of a series of five

    low-energy laser pulses with energy density E1

    1.0

    102 Jcm2. The fusion threshold was not attained upon irradi-

    ation with this energy density, and the surface of the test

    piece did not change. The material fused under a high-inten-

    sity pulsed action with energy density E2

    6 102 Jcm2.

    The time of the start of the melting process was determined

    from the decline of the intensity of the signal reflected from

    the surface of the alloy during the action of a laser pulse [2].

    The tests were performed in the following mode. We sin-

    gled out three regions on the surface of the test piece.

    In the first region we determined the effect of the prelim-

    inary laser irradiation on the start of the process of fusion of

    the alloy. This region was subjected to irradiation with low-

    energy laser pulses (five pulses) with energy density E1. We

    detected the time of the start of fusion in subsequent irradi-

    ation of this region with a pulse with energy density E2. The

    obtained time was compared with the time of the start of fu-

    sion of the alloy under the action of a laser pulse with energy

    density E2

    without preliminary low-energy irradiation.

    The second region was subjected to irradiation with

    low-energy laser pulses with energy density E1. Then the test

    piece was annealed at a temperature of 300C for 2 h and

    cooled with the furnace. After the annealing the second re-

    gion was irradiated with high-energy laser pulses with en-

    ergy density E2, and the time of the start of fusion was de-

    tected.

    In the third region of the test pieces, which had been sub-

    jected to annealing, we again determined the effect of the

    preliminary low-energy laser irradiation on the start of the

    Metal Science and Heat Treatment, Vol. 55, Nos. 7 8, November, 2013 (Russian Original Nos. 7 8, July August, 2013)

    368

    0026-0673/13/0708-0368 2013 Springer Science + Business Media New York

    1Institute for Problems of Mechanical Engineering of the Russian

    Academy of Sciences (IPM RAN), Nizhny Novgorod, Russia

    (e-mail: [email protected]).

  • melting process under the action of a high-energy laser pulse.

    For this purpose the surface of the third region of an an-

    nealed test piece was first subjected to the action of low-

    energy laser pulses and then irradiated with a laser pulse that

    caused fusion of the alloy at energy density E2. The detected

    time before the start of fusion of the test piece was compared

    with the time of the start of fusion in this region only under

    irradiation with energy density E2.

    RESULTS AND DISCUSSION

    The mean values of the times of the start of fusion of al-

    loy 1421 in different regions of test pieces are presented in

    Table 1. Analyzing the results we established the following.

    The time before the start of fusion of the alloy with prelimi-

    nary low-energy treatment under the action of high-energy

    laser irradiation was shorter than without such treatment (see

    the first region before annealing in Table 1).

    In the second region of the test piece, which had been

    subjected to a preliminary treatment, the action of the high-

    intensity laser pulse after annealing did not cause shortening

    of the time before the start of fusion. The time before the

    start of fusion of the material in the third region turned out to

    be equal to the time of the start of fusion of the alloy in the

    first region without preliminary treatment (see the second re-

    gion in Table 1, after annealing). Thus, the annealing removed

    the effect of the preliminary laser treatment on the time of the

    start of fusion of the alloy under the action of a high-intensity

    laser pulse. The third region of the test piece was also an-

    nealed. Preliminary treatment of this region again shortened

    the time before the start of fusion of the alloy under the ac-

    tion of subsequent high-intensity laser irradiation as com-

    pared to the action of only a high-intensity laser pulse on this

    region (see the third region in Table 1, after annealing).

    The results obtains are explainable by the effect of the

    concentration of nonequilibrium vacancies on the start of fu-

    sion of the alloy. The concentration of nonequilibrium vacan-

    cies increases under the action of preliminary low-energy la-

    ser pulses on the surface of the alloy. The growth in the con-

    centration may be a result of (a) an increase in the concentra-

    tion of thermal fluctuation vacancies [3] and (b) an increase

    in the concentration of vacancies due to growth of the oxide

    film [4]. In the short time of the action of a laser pulse

    (10 3 sec) and in about the same time of cooling the major

    part of vacancies do not have enough time for going into

    sinks, and the material preserves frozen nonequilibrium

    vacancies.

    Growth in the concentration of nonequilibrium vacancies

    increases the absorptivity of the material connected with ad-

    ditional scattering of conduction electrons in the skin layer of

    the alloy [5]. Annealing and slow cooling bring the concen-

    tration of vacancies to equilibrium due to their sinking (for

    example onto grain boundaries), which is responsible for dis-

    appearance of the mentioned influence of the preliminary la-

    ser treatment on the time of the start of fusion. Preliminary

    low-power treatment of the alloy subjected to annealing has

    also caused accumulation of vacancies in the near-surface

    layer, growth in the absorptivity, and decrease in the time of

    the start of fusion.

    CONCLUSIONS

    Annealing of aluminum alloy 1421 irradiated prelimina-

    rily by a series of low-energy laser pulses causes disappear-

    ance of the influence of preliminary treatment on the time of

    the start of fusion of the alloy under high-intensity laser irra-

    diation.

    The authors are sincerely grateful to V. N. Perevezentsev

    for the helpful discussion of the results of this work.

    REFERENCES

    1. P. Yu. Kikin, V. N. Perevezentsev, E. E. Rusin, and E. N. Razov,

    Effect of preliminary high-power laser irradiation on the pro-

    cess of melting of aluminum alloys, Zh. Teor. Fiz., 82(2),

    46 49 (2012).

    2. P. Yu. Kikin, V. N. Perevezentsev, A. I. Pchelintsev, and E. E. Ru-

    sin, Treatment of ultrafine-grained aluminum alloys by pulsed

    laser irradiation, Prob. Mashonostr. Nadezhn. Mash., No. 5,

    87 91 (2007).

    3. Ya. I. Frenkel, An Introduction into the Theory of Metals [in Rus-

    sian], Izd. Tekhn.-Teor. Literatury, Moscow (1950), 383 p.

    4. N. Henney, The Solid State Chemistry [Russian translation], Mir,

    Moscow (1971), 223 p.

    5. F. Kh. Mirzoev, V. Ya. Panchenko, and L. A. Shelepin, Laser

    control of processes in a solid, Usp. Fiz. Nauk, 166(1), 3 32

    (1996).

    Effect of Annealing on Preliminary Treatment of Aluminum Alloy 1421 By Low-Energy Laser Pulses 369

    TABLE 1. Time of the Start of Fusion of Alloy 1421 under Pulsed Laser Irradiati