Precipitation and Hardening in Magnesium Alloys

Abstract

Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

The Effect of Deep Cryogenic Treatment on the Corrosion Behavior of Mg-7Y-1.5Nd Magnesium Alloy

“…The results shown in Figure 8 indicated that α-Mg was the major phase, and that the precipitated phases of the as-cast, T4 and T6 samples both contain Mg 24 (Y, Nd) 5 and Mg 3 (Y, Nd); this findings is consistent with Nie's results [13,33]. "Undissolved particles" remained after the solidification process, as shown in Figure 3.…”

“…Various precipitations (e.g., Mg 3 Nd, Mg 12 YNd, Mg 3 (Y, Nd), etc.) may form in a Mg-Y-Nd system [13]. The majority of previous studies have focused on the relationship between precipitations and mechanical strength.…”

The Microstructures and Tensile Properties of As-Extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) Alloys

“…Therefore, the basal precipitates are proposed to have a hexagonal structure with a = 0.556 nm. It is well known that precipitation strengthening is an effective way to strengthen Mg alloy, however, many investigations about precipitation focus on the static precipitation, especially Mg-RE alloys [15,18,26,27]. As mentioned by Kabir [22], the formation of strain-induced precipitates depended on deformation temperature, strain, and strain rate.…”

Aging Effect of Mg-Sc Alloy with α+β Two-Phase Microstructure

“…These results indicate that it is possible to enhance the mechanical properties of the age-hardened Mg-Sc alloy by controlling the initial microstructure. Figure 6 shows the relationship between the UTS and ultimate tensile elongation in various precipitation-strengthened magnesium alloys with an ultimate tensile elongation of over 5%, where those magnesium alloys were categorized by their production processes into casting, extrusion, equal channel angular pressing (ECAP) and rolling 17,18) . The present age-hardened Mg-Sc alloys show mechanical properties comparable to those of reported high strength magnesium al- loys.…”