Truck & Off-Highway Engineering - April 2021 - 7

Material selection for
battery enclosures

MATERIALS FEATURE

Light weight is a definite consideration for
the Freightliner eCascadia's battery-enclosure design,
which employs aluminum, but durability also is a critical factor.

Mass reduction is the main reason BEV makers choose aluminum for battery
enclosures, but cost and thermal requirements favor steel and polymer composites.

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luminum is the dominant material for electric
vehicle (EV) battery enclosures for one simple
but significant factor: lightweighting capability.
All currently available long-range BEVs - those
that can travel beyond 250 miles (400 km) - use aluminum as the main material for the battery enclosure for
that very reason, Dr. Andreas Afseth, technical director
for Constellium North America operations, said during a
recent Center for Automotive Research (CAR) webinar.
" Aluminum continues to be the fastest-growing material in automotive application, " Afseth said. Growth is driven in part by the increasing market share of BEVs, including electric trucks and vans, which already employ a
greater amount of aluminum than do conventional-powertrain models - more than 640 lb (290 kg) in BEV platforms compared to about 450 lb (205 kg) in non-BEVs.
" Electric trucks will require very large batteries,
maximum payload and minimum energy consumption
(operating costs), " he said. " There will continue to be a
very high value of lightweighting, so I would expect
aluminum to be the material of choice. " (See sidebar.)
Aluminum battery enclosures or other platform
parts typically provide a weight savings of 40% compared to an equivalent steel design. The most-used
and best-suited alloys for battery enclosures are of the
6000-series Al-Si-Mg-Cu family, Afseth shared, noting
TRUCK & OFF-HIGHWAY ENGINEERING

that these alloys are " very well compatible " with end-of-life recycling.
The current state-of-the-art solution for bottom plates is highstrength 6111 alloy in peak aged temper, which reduces weight by
30% compared to the benchmark 5754 O-temper alloy.
Constellium has a 4xxx alloy in development with 80-GPa
E-modulus and 350-MPa yield stress. A 40% weight reduction is
" technically feasible " with the developmental 4xxx alloy. " You can
think of this high-modulus 4000 series alloy as a 'very excess' silicon
6000 series alloy, " Afseth said, noting that gauges and widths will be
similar to 6000. It is compatible with conventional cold forming and
is cost-competitive, he said.
A 7075 T6 alloy also in development offers 500-MPa yield stress and
70-GPa E-modulus. 7000-series alloys of Al-Zn-Mg-Cu are not yet widely
used in automotive application, he noted. 7000 could be considered for
bottom plates where impact resistance is key, but a point of " diminishing
returns " likely will hinder its use in this application. " At the moment, with
the manufacturing processes needed, this [additional 10% weight savings] benefit probably doesn't cover the cost of using 7000, " Afseth said.

Enclosure design
The battery enclosure has a critical role in crash energy management,
both in terms of preventing intrusion into the battery cells as well as
absorbing energy to protect the occupants. A dual-frame prototype
for passenger vehicles illustrated by Constellium employs two different advanced extruded alloys. The inner frame is made of strengthApril 2021 7

DAIMLER TRUCKS NORTH AMERICA

by Ryan Gehm

Truck & Off-Highway Engineering - April 2021

Table of Contents for the Digital Edition of Truck & Off-Highway Engineering - April 2021