Grain Boundary and Intragranular Reactions during Aging in Mg-Al System Alloys Poured into Sand and Iron Molds

Abstract

It is well-known that age hardening occurs in Mg-Al system alloys, when the alloy containing aluminum exceeds 6 mass%. This precipitation reaction depends on the aluminum content and aging temperature. The aging behavior in AZ91 magnesium alloy was investigated and it is the subject of this paper. However, for the Mg-Al system alloys, the influence of aluminum content on age hardening characteristics has not been researched in detail so far. In this study, continuous and discontinuous precipitations during aging in Mg-Al system alloys cast into sand and iron molds was investigated by means of hardness measurement and microstructure observation with optical microscope and transmission electron microscope. The microstructure of AM60 magnesium alloy with 6 mass% containing aluminum in the as cast condition was composed with a primary crystallized alpha magnesium phase and beta Mg 17 Al 12 phase. The hardness of cellular precipitates existing near the grain boundary in sand mold castings decreased with increasing the aging time. On the other hand, the hardness of intragranular precipitates was constant against the aging time. Variation of hardness with aging was found to be caused mainly by the discontinuous precipitation along the grain boundaries from the composite rule in hardness. In iron mold castings, it was found that the variation of hardness with aging was found to be caused mainly by the continuous precipitation inside the crystal grain.

Texture and stretch formability of AZ61 and AM60 magnesium alloy sheets processed by high-temperature rolling

“…Compared to that of a previous AZ31 alloy processed by hightemperature rolling [8], the AM60 alloy exhibits a similar stretch formability (8.5 mm vs. 8.6 mm for the Erichsen value) but a higher UTS (268 MPa vs. 258 MPa in average). Furthermore, it is possible to enhance the mechanical strength of the AM60 alloy further by age hardening owing to its high Al content [12].…”

“…Furthermore, additional material strengthening can be obtained through aging treatments owing to the precipitation of the Mg 17 Al 12 phase in both the AZ61 and AM60 alloys [11,12]. This is a desirable approach for material strengthening because it can be performed after sheet forming [10,13].…”

Texture, Microstructure, and Mechanical Properties of Calcium- Containing Flame-Resistant Magnesium Alloy Sheets Produced by Twin-Roll Casting and Sequential Warm Rolling

“…The amount of wrought materials that are used is low, representing less than 10% of all Mg alloys that are used [10]. Recently, the problems associated with Mg alloys have been resolved by increasing their strength [11][12][13] and by improving their creep properties [14], heat resistance [15], and formability [16,17] by adding trace amounts of various elements [18,19], by age-hardening effects [20], by crystal-grain refinement [21,22], and by texture control [23,24]. However, there is still a need for incombustible or noncombustible Mg alloys [25][26][27] for use in structural or construction components.…”