Making a Case for B206


Casting trials for a modifi ed 206 aluminum alloy that approaches the strength of ductile iron without hot cracking produced encouraging results.


Andres Rodriguez, Ruben Chavez and Jacobo Hernandez, Nemak, S.A., Nuevo Leon, Mexico Yves Raymond, Rio Tinto Alcan, Jonquiere, Quebec, Canada J. Fred Major, Rio Tinto Alcan, Kingston, Ontario, Canada


A


luminum alloy A206 pos- sesses several character- istics that seem perfectly suited for automotive ap- plications. Its mechanical


properties approach that of ductile iron grades commonly used to cast ferrous automotive suspension parts, thus pro- viding opportunity for reducing vehicle weight. But one fl aw eliminates A206 from material selection—its propensity for hot cracking, which is a defect formed on the surface of a casting due to internal stress caused by cooling during solidifi cation. A version of the alloy recently


has been developed to address its shortcomings. Reducing the amount of titanium in the alloy has been found to result in a better response to titanium-boron grain refi ners, which are added to liquid metal to aid in producing a fi ner grain size in the


Aluminum B206 could replace some duc- tile iron automotive applications to help lighten vehicles (above).


March/april 2010


Table 1. Alloys Cast and Results of Permanent Mold Hot Tear Test Alloy Crack Rating % Cu % Mg % Mn %Fe A1 A2 A3 A4 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 D1 D2 D3 D4 D5 D6


2.6


2.55 2.7


2.85 2.8 2.7 3.2


2.75 3.25 3


2.25 3.05 2.8


2.25 3


2.8


3.15 2.85 3.45 2.75


3.63 3.57 3.8


3.75 3.9


4.03 3.93


3.915 4.02 4.51 4.52 4.35 4.48 4.47 4.9 4.9 4.9


5.06 4.77 4.81


0.083 0.225 0.471 0.42


0.064 0.195 0.176 0.166 0.161 0.184 0.235 0.24 0.24


0.238 0.302 0.47


0.472 0.493 0.487 0.479


0 0 0 0 0 0 0 0


0.344 0.08


0.217 0.234 0.239 0.234 0.239 0.238 0.432 0.452 0.448 0.447


0.069 0.069 0.078 0.07


0.067 0.068 0.222 0.215 0.215 0.106 0.098 0.221 0.235 0.236 0.069 0.068 0.068 0.07


0.256 0.26


% Si %Zn 0.06 0.07 0.07 0.08


0.065 0.06 0.06


0.215 0.18 0.08 0.09 0.05


0.145 0.16 0.05 0.05 0.08 0.1 0.1


0.23


0.046 0.005 0.005 0.21


0.043 0.026 0.018 0.016 0.015 0.005 0.005 0.006 0.01


0.202 0.005 0.005 0.005 0.22


0.197 0.197


Metal casting Design anD purchasing 37


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