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Lead-induced solid metal embrittlement of aluminum-magnesium-silicon alloys at ambient temperatures

Kim, Young-Sub

Abstract Details

1990, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Minute amounts of Pb(i.e. 5ppm-500ppm) are shown to induce embrittlement of Al-Mg-Si alloys at ambient temperatures. In the high Pb alloys (i.e. >100 ppm), Pb was usually associated with particles containing Si, Mn and Fe although isolated Pb signals were often found on the grain boundary. In the low Pb alloys (i.e. <20ppm), Pb was only found in association with Fe-containing particles. These sites of high Pb concentration are preferential sites for crack initiation. It was observed in the tensile tests that grain boundary accommodation of deformation was predominant in the early stage of tensile deformation in high Pb alloys tested at slow strain rate, in contrast to transgranular slip which was predominant in specimens containing low Pb and/or those tested at fast strain rates. Intergranular microvoid coalescence (IGMVC) was predominant in the fracture mode of the high Pb alloys tested at fast strain rate and the low Pb alloys tested at both strain rates, while low ductility intergranular fracture (LDIGF) was predominant in the higher Pb alloys tested at slow strain rate. It is proposed that locally segregated regions of Pb are preferential sites for cracking in a LDIGF mode either by decohesion or cracking of Pb-containing particles, with subsequent Pb-assisted propagation oc curring along grain boundaries. Propagation of fracture in a LDIGF mode requires a continual supply of Pb to the crack tip region, as supported by the tensile interruption tests and the external Pb tests which conclusively showed the increase in the amount of LDIGF, the decrease in the non-uniform strain and increase in crack growth rate. In-situ deformation in SEM confirmed the effects of Pb on fracture behavior. The possible mechanisms are discussed in the regard of the crack tip strain rate, the semicohesive zone ahead of crack and the Pb surface diffusion, in addition to the reduction of surface energy by the addition of Pb.
John Lewandowski (Advisor)
291 p.

Recommended Citations

Citations

  • Kim, Y.-S. (1990). Lead-induced solid metal embrittlement of aluminum-magnesium-silicon alloys at ambient temperatures [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1054843940

    APA Style (7th edition)

  • Kim, Young-Sub. Lead-induced solid metal embrittlement of aluminum-magnesium-silicon alloys at ambient temperatures. 1990. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1054843940.

    MLA Style (8th edition)

  • Kim, Young-Sub. "Lead-induced solid metal embrittlement of aluminum-magnesium-silicon alloys at ambient temperatures." Doctoral dissertation, Case Western Reserve University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054843940

    Chicago Manual of Style (17th edition)