Abstract
Lightweight sheet alloys with superior mechanical performance such as high strength, ductility and formability at room temperature (RT) are desirable for high volume automotive applications. However, ductility or formability of metallic alloys at RT are generally inversely related to strength, thereby making it difficult to optimize all three simultaneously. Here we design a new magnesium sheet alloy-ZAXME11100 (Mg-1.0Zn-1.0Al-0.5Ca-0.4Mn-0.2Ce, wt. pct.) via CALPHAD (CALculation of PHAse Diagram) modeling and experimental validation. This new sheet alloy offers an excellent RT formability with a high Index Erichsen (I.E.) value of 7.8 mm in a solution-treated condition (T4), due to its weak and split basal texture and fine grain structure. The new ZAXME 11100 alloy also shows a rapid age-hardening response during post-forming artificial aging treatment at 210 °C for 1 hour (T6), resulting in a significant increase of yield strength from 159 MPa (T4) to 270 MPa (T6). The excellent combination of T4 ductility (31%), T4 formability (7.8 mm) and T6 yield strength (270 MPa) in this new magnesium alloy is comparable to that of common 6xxx series aluminum sheet alloys. Thus, this new magnesium sheet alloy is highly attractive for sheet applications in automotive and other industries.
Highlights
Lightweight sheet alloys with superior mechanical performance such as high strength, ductility and formability at room temperature (RT) are desirable for high volume automotive applications
The results show that HCP Mg phase will form as a primary phase at 638 °C, followed by the formation of Al8Mn5, Mg12Ce, Al2Ca, Ca2Mg5Zn5, Ce2Mg53Zn45, Al11Mn4 and Ca2Mg5Zn13 phases at 628 °C, 546 °C, 488 °C, 368 °C, 357 °C, 329 °C and 325 °C, respectively
The results showed that the second phase particles near and along the grain boundaries have been essentially dissolved after the new homogenization profile (H480)
Summary
Lightweight sheet alloys with superior mechanical performance such as high strength, ductility and formability at room temperature (RT) are desirable for high volume automotive applications. The excellent combination of T4 ductility (31%), T4 formability (7.8 mm) and T6 yield strength (270 MPa) in this new magnesium alloy is comparable to that of common 6xxx series aluminum sheet alloys. Compared to 6xxx series aluminum alloys[5,6] or steels[7], inferior mechanical properties at RT and high processing cost limit wider applications of commercial Mg sheet alloys such as AZ31 (Mg-3Al-1Zn-0.3Mn) and ZE10 (Mg-1Zn-0.2Ce)[8,9]. This is the well-known issue of the “strength-formability trade-off dilemma” in Mg and other sheet alloys. The combination of the new alloy design and the multi-stage TMP process leads to the optimum combination of strength, ductility and formability of the new alloy
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